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Weed interference and weed control in cole crops and onion Bitterlich, Iris 1990

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WEED INTERFERENCE AND WEED CONTROL IN COLE CROPS AND ONION By IRIS BITTERLICH B . S c , The U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1987 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department o f P l a n t S c i e n c e ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1990 © I r i s B i t t e r l i c h , 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada DE-6 (2/88) i i A b s t r a c t A d d i t i v e weed c o m p e t i t i o n e x p e r i m e n t s were u n d e r t a k e n t o s t u d y t h e e f f e c t o f l a m b ' s - q u a r t e r s {Chenopodium album) i n t e r f e r e n c e on d i r e c t s e e d e d b r o c c o l i . L a m b ' s - q u a r t e r s ( 3 , 8, 10, 12, and 15 p l a n t s n f 2 ) began t o a f f e c t b r o c c o l i growth 28 t o 36 days a f t e r s e e d i n g . Decreases i n c r o p g r o w t h i n c r e a s e d w i t h weed d e n s i t y as t i m e a f t e r s e e d i n g i n c r e a s e d . Y i e l d d a t a were f i t t e d t o a r e c t a n g u l a r h y p e r b o l i c model w h i c h i n d i c a t e d t h a t even one l a m b ' s - q u a r t e r s p l a n t m~2 c o u l d r e d u c e t o t a l y i e l d by 18 t o 20 p e r c e n t and m a r k e t a b l e y i e l d ( h e a d >10 cm a c r o s s ) by 22 t o 37 p e r c e n t . L a m b ' s - q u a r t e r s r e d u c e d t o t a l y i e l d by r e d u c i n g average head w e i g h t and not by l o w e r i n g t h e number o f heads per p l o t . On t h e o t h e r hand, t h e weed re d u c e d m a r k e t a b l e y i e l d by r e d u c i n g both t h e average head w e i g h t and t h e number o f heads p e r p l o t . T h e f e a s i b i l i t y o f u s i n g l i q u i d ammonium n i t r a t e a s a p o s t - e m e r g e n t weed c o n t r o l s p r a y i n c o l e c r o p s was s t u d i e d . The r e l a t i v e s u s c e p t i b i l i t y o f d i f f e r e n t weed s p e c i e s grown by t h e m s e l v e s (1989) and w i t h two c r o p s ( b r o c c o l i and o n i o n ; 1987) t o ammonium n i t r a t e (800 L h a " 1 ; 0, 7.5, 10, 15, 20 p e r c e n t N) b u r n i n g was i n v e s t i g a t e d . The f e r t i l i z e r c o n t r o l l e d s h e p h e r d ' s - p u r s e (Capsella bursa-pastoris), c h i c k w e e d (Stel 1 an' a media), cudweed {Gnaphalium uliginosum), and r e d r o o t p i g w e e d (Amaranthus retroflexus), b u t n o t l a m b ' s - q u a r t e r s , p u r s l a n e (Portulaca oleracea), and annual b l u e g r a s s {Poa annua). Corn s p u r r y (Spergula arvensis) v a r i e d i n i t s t o l e r a n c e . A l t h o u g h weed p o p u l a t i o n s were r e d u c e d by 70 p e r c e n t i n 1987, t h e r e m a i n i n g weeds i i i competed so s t r o n g l y w i t h t h e o n i o n and b r o c c o l i t h a t t h e c r o p p l a n t s d i d n o t r e a c h a h a r v e s t a b l e s i z e . The l a r g e i n i t i a l weed p o p u l a t i o n (799 p l a n t s n f 2 ) , t h e l a r g e number o f t o l e r a n t weeds p r e s e n t , and t h e p o s s i b l e r e c o v e r y o f some o f t h e s u s c e p t i b l e weeds may a l l have been f a c t o r s r e s p o n s i b l e f o r c r o p f a i l u r e . The e f f e c t o f d i f f e r e n t s h e p h e r d ' s - p u r s e d e n s i t i e s (52 t o 988 p l a n t s m"2) on t h e degree o f ammonium n i t r a t e (800 L ha" 1; 20 p e r c e n t N) c o n t r o l i n b r o c c o l i was a l s o s t u d i e d . The i n i t i a l weed c o n t r o l a c h i e v e d was r e d u c e d o v e r t i m e e i t h e r b e c a u s e some weeds c o u n t e d as dead had r e c o v e r e d o r new p l a n t s were b e i n g r e c r u i t e d t o t h e p o p u l a t i o n t h r o u g h s e e d g e r m i n a t i o n . A l t h o u g h t h e maximum d e n s i t y o f s h e p h e r d ' s - p u r s e p l a n t s t h a t s u r v i v e d was 219 p l a n t s n f 2 , t h e s e p l a n t s d i d n o t s i g n i f i c a n t l y r e d u c e c r o p y i e l d p o s s i b l y because s h e p h e r d ' s - p u r s e i s not a v e r y c o m p e t i t i v e s p e c i e s and a l l t h e s u r v i v i n g weeds had been damaged t o v a r y i n g d e g r e e s , f u r t h e r r e d u c i n g t h e i r c o m p e t i t i v e a b i l i t y . The r e l a t i v e s u s c e p t i b i l i t y o f v a r i o u s c r o p c u l t i v a r s t o ammonium n i t r a t e (800 L ha" 1; 0, 10, 15, 20 p e r c e n t N) b u r n i n g was a l s o s t u d i e d . I n 1 9 8 7 , t h e g r o w t h r a t e s o f ' L u n e t ' ( B r u s s e l s s p r o u t s ) , x S G I ' ( b r o c c o l i ) , ' E l g o n ' ( c a u l i f l o w e r ) , and 'Matra' ( c a u l i f l o w e r ) i n i t i a l l y d e c r e a s e d b u t t h e p l a n t s r e c o v e r e d ; t h e y were l a r g e l y u n a f f e c t e d i n 1988. The growth r a t e s o f 'White L i s b o n ' ( o n i o n ) , 'Emperor' ( b r o c c o l i ) , and ' E a r l y M a r v e l ' ( c a b b a g e ) were l a r g e l y u n a f f e c t e d i n e i t h e r y e a r . A l t h o u g h some c u l t i v a r s had shown i n i t i a l s i g n s o f l o w e r growth r a t e s , t h e r e was no d e c r e a s e i n c r o p y i e l d . i v L e a f s u r f a c e s o f t o l e r a n t and s u s c e p t i b l e c r o p and weed s p e c i e s were examined by s c a n n i n g e l e c t r o n m i c r o s c o p y t o d e t e r m i n e t h e b a s i s o f ammonium n i t r a t e s e l e c t i v i t y . L e a f s u r f a c e s o f t o l e r a n t s p e c i e s were c o m p l e t e l y c o v e r e d w i t h a c r y s t a l l i n e wax l a y e r , w h i l e s u s c e p t i b l e s p e c i e s had l i t t l e o r no e p i c u t i c u l a r wax. C e l l u l o s e a c e t a t e was used t o remove t h e e p i c u t i c u l a r wax from cabbage l e a v e s . The s t r i p p e d l e a v e s showed f a r g r e a t e r ammonium n i t r a t e r e t e n t i o n and s a l t i n j u r y t h a n u n s t r i p p e d l e a v e s , d e m o n s t r a t i n g t h e i m p o r t a n c e o f t h e e p i c u t i c u l a r wax i n p r o v i d i n g p r o t e c t i o n a g a i n s t ammonium n i t r a t e i n j u r y . T r i c h o m e s , o b s e r v e d on t h e l e a f s u r f a c e s o f some s u s c e p t i b l e s p e c i e s , may f u r t h e r i n c r e a s e ammonium n i t r a t e r e t e n t i o n and, t h e r e f o r e , s a l t i n j u r y . V T a b l e o f C o n t e n t s A b s t r a c t . i i T a b l e o f C o n t e n t s v L i s t o f T a b l e s v i i L i s t o f F i g u r e s v i i i L i s t o f A p p e n d i c e s x Acknowl edgement x i 1. I n t r o d u c t i o n 1 2. L i t e r a t u r e Review 5 2.1 Weed I n t e r f e r e n c e 5 ( i ) C o m p e t i t i o n f o r L i m i t e d R e s o u r c e s 5 ( i i ) A l l e l o p a t h y 8 ( i i i ) S h i f t i n g t h e B a l a n c e 8 ( i v ) S t u d y i n g Weed I n t e r f e r e n c e 10 2.2 Weed C o n t r o l S t r a t e g i e s 12 2.3 Post-emergent Weed C o n t r o l i n C o l e Crops and Onion w i t h N i t r o g e n F e r t i l i z e r s 14 3. L a m b ' s - q u a r t e r s I n t e r f e r e n c e W i t h D i r e c t Seeded B r o c c o l i 26 3.1 I n t r o d u c t i o n 26 3.2 M a t e r i a l s and Methods 26 3.3 R e s u l t s and D i s c u s s i o n ; 28 4. Weed c o n t r o l i n C o l e Crops and Onion U s i n g an Ammonium N i t r a t e S o l u t i o n 42 4.1 I n t r o d u c t i o n 42 v i 4.2 R e l a t i v e S u s c e p t i b i l i t y o f D i f f e r e n t Weed S p e c i e s and t h e E f f e c t o f S h e p h e r d ' s - p u r s e D e n s i t y on Weed C o n t r o l 43 ( i ) M a t e r i a l s and Methods 43 ( i i ) R e s u l t s and D i s c u s s i o n 47 4.3 R e l a t i v e S u s c e p t i b i l i t y o f C o l e and Onion C u l t i v a r s 63 ( i ) M a t e r i a l s and Methods 63 ( i i ) R e s u l t s and D i s c u s s i o n 65 5. L e a f S u r f a c e U l t r a s t r u c t u r e and S u s c e p t i b i l i t y t o Ammonium N i t r a t e I n j u r y 81 5.1 I n t r o d u c t i o n 81 5.2 M a t e r i a l s and Methods 82 5.3 R e s u l t s and D i s c u s s i o n 83 6. C o n c l u s i o n 93 7. B i b l i o g r a p h y 95 A p p e n d i x 1 102 Ap p e n d i x 2 104 Ap p e n d i x 3 106 Ap p e n d i x 4 107 Ap p e n d i x 5 108 Ap p e n d i x 6 109 Ap p e n d i x 7 110 A p p e n d i x 8 I l l v i i List o f Tables T a b l e 1. The number o f t o t a l and m a r k e t a b l e heads p e r p l o t i n 1987 and 1988... 36 T a b l e 2. E f f e c t o f ammonium n i t r a t e on m a r k e t a b l e y i e l d s o f c o l e c r o p s and o n i o n 79 T a b l e 3. E f f e c t o f ammonium n i t r a t e on p e r p l a n t y i e l d o f c o l e c r o p s and o n i o n 80 v i i i L i s t o f F i g u r e s F i g . 1 T i m e - c o u r s e o f t h e e f f e c t o f 1 a m b ' s - q u a r t e r s d e n s i t i e s on b r o c c o l i s h o o t d r y w e i g h t i n 1987 and 1988 29 F i g . 2 The e f f e c t o f l a m b ' s - q u a r t e r s d e n s i t i e s on t o t a l and m a r k e t a b l e y i e l d f o r 1987 and 1988 32 F i g . 3 L a m b ' s - q u a r t e r s and b r o c c o l i a t (a) 31 days and ( b ) 43 d a y s a f t e r s e e d i n g ( 1 9 8 8 ) s h o w i n g d i f f e r e n c e s i n growth 34 F i g . 4 R e l a t i v e h e i g h t o f l a m b ' s - q u a r t e r s and b r o c c o l i a t 31 days and 43 days a f t e r s e e d i n g (1988) 39 F i g . 5. P e r c e n t weed c o n t r o l i n 1987 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s ( p e r c e n t N) a t 2 and an aver a g e o f 46 days a f t e r a p p l i c a t i o n 48 F i g . 6. P e r c e n t weed c o n t r o l i n 1988 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s ( p e r c e n t N) a t 4 and 12 days a f t e r a p p l i c a t i o n 50 F i g . 7. S u s c e p t i b l e and t o l e r a n t weed s p e c i e s 2 d a y s a f t e r ammonium n i t r a t e (20 p e r c e n t N) a p p l i c a t i o n 52 F i g . 8. The e f f e c t o f s h e p h e r d ' s - p u r s e d e n s i t y on i t s c o n t r o l by ammonium n i t r a t e (20 p e r c e n t N) 56 F i g 9. S h e p h e r d ' s - p u r s e c o n t r o l by ammonium n i t r a t e ( 2 0 p e r c e n t N ) : b e f o r e a n d a f t e r ammonium n i t r a t e a p p l i c a t i o n 58 F i g . 10. A s m a l l p e r c e n t a g e o f s h e p h e r d ' s - p u r s e p l a n t s , w h i c h were not c o m p l e t e l y b u r n t , resumed growth and r e c o v e r e d 60 F i g . 11. P e r c e n t r e l a t i v e g r o w t h ( l o g d r y wt i n g) f o r X S G 1 ' ( b r o c c o l i ) , ' L u n e t ' ( B r u s s e l s s p r o u t s ) , ' M a t r a ' ( c a u l i f l o w e r ) , and ' E l g o n ' ( c a u l i f l o w e r ) i n 1 9 8 7 f o r d i f f e r e n t a m m o n i u m n i t r a t e c o n c e n t r a t i o n s (10, 15, and 20 p e r c e n t N) 66 F i g . 12. P e r c e n t r e l a t i v e g r o w t h ( l o g d r y wt i n g) f o r VSG1' ( b r o c c o l i ) , v L u n e t ' ( B r u s s e l s s p r o u t s ) , ' M a t r a ' ( c a u l i f l o w e r ) , and v E l g o n ' ( c a u l i f l o w e r ) i n 1 9 8 8 f o r d i f f e r e n t a m m o n i u m n i t r a t e c o n c e n t r a t i o n s (10, 15, and 20 p e r c e n t N) 68 i x F i g . 13. P e r c e n t r e l a t i v e g r o w t h ( l o g d r y wt i n g) f o r ' W h i t e L i s b o n ' ( o n i o n ) , ' E a r l y M a r v e l ' ( c a b b a g e ) , and 'Emperor' ( b r o c c o l i ) i n 1987 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s (10, 15, and 20 p e r c e n t N) 72 F i g . 14. P e r c e n t r e l a t i v e g r o w t h ( l o g d r y wt i n g) f o r ' W h i t e L i s b o n ' ( o n i o n ) , ' E a r l y M a r v e l ' ( c a b b a g e ) , and 'Emperor' ( b r o c c o l i ) i n 1988 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s ( 1 0 , 15, and 20 p e r c e n t N) 74 F i g . 15. B r o c c o l i ( c v . E m p e r o r ) 15 m i n u t e s and 2 d a y s a f t e r a m m o n i u m n i t r a t e ( 2 0 p e r c e n t N) a p p l i c a t i o n (1988) 76 F i g 16. L e a f s u r f a c e ( a d a x i a l ) morphology o f s u s c e p t i b l e weed s p e c i e s 84 F i g . 17. C r y s t a l l i n e e p i c u t i c u l a r wax d e p o s i t i o n on t h e a d a x i a l l e a f s u r f a c e o f t o l e r a n t s p e c i e s 87 F i g . 18. S u r f a c e o f t h e 1 s t t r u e - l e a f o f cabbage w i t h and w i t h o u t c r y s t a l l i n e e p i c u t i c u l a r w a x ; c o m p a r i s o n o f s o l u t i o n r e t e n t i o n by s t r i p p e d and u n s t r i p p e d l e a v e s o f cabbage i m m e d i a t e l y a f t e r ammonium n i t r a t e a p p l i c a t i o n ; and c o m p a r i s o n o f f o l i a r i n j u r y i n u n s t r i p p e d and s t r i p p e d cabbage p l a n t s 4 d a y s a f t e r s p r a y i n g w i t h ammonium n i t r a t e s o l u t i o n 89 X L i s t o f A p p e n d i c e s A p p e n d i x 1. R e l a t i v e s u s c e p t i b i l i t y o f weed s p e c i e s i n 1987. R e g r e s s i o n a n a l y s i s o f weed numbers b e f o r e and a f t e r ammonium n i t r a t e a p p l i c a t i o n 102 A p p e n d i x 2. R e l a t i v e s u s c e p t i b i l i t y o f weed s p e c i e s i n 1989. R e g r e s s i o n a n a l y s i s o f weed numbers b e f o r e and a f t e r ammonium n i t r a t e a p p l i c a t i o n 104 A p p e n d i x 3. S h e p h e r d ' s - p u r s e d e n s i t y a n d weed c o n t r o l e x p e r i m e n t . R e g r e s s i o n a n a l y s i s o f s h e p h e r d ' s - p u r s e numbers a f t e r ammonium n i t r a t e a p p l i c a t i o n 106 A p p e n d i x 4. S h e p h e r d ' s - p u r s e d e n s i t y a n d weed c o n t r o l e x p e r i m e n t . R e g r e s s i o n a n a l y s i s o f b r o c c o l i g rowth and y i e l d 107 A p p e n d i x 5. R e l a t i v e s u s c e p t i b i l i t y o f c r o p c u l t i v a r s i n 19 8 7 . R e g r e s s i o n a n a l y s i s o f c u l t i v a r d r y w e i g h t s a f t e r ammonium n i t r a t e a p p l i c a t i o n 108 A p p e n d i x 6. R e l a t i v e s u s c e p t i b i l i t y o f c r o p c u l t i v a r s i n 1 9 8 8 . R e g r e s s i o n a n a l y s i s o f c u l t i v a r d r y w e i g h t s a f t e r ammonium n i t r a t e a p p l i c a t i o n 109 Ap p e n d i x 7. R e l a t i v e s u s c e p t i b i l i t y o f c r o p c u l t i v a r s . R e g r e s s i o n a n a l y s i s o f c r o p y i e l d 110 Ap p e n d i x 8. R e l a t i v e s u s c e p t i b i l i t y o f c r o p c u l t i v a r s . R e g r e s s i o n a n a l y s i s o f y i e l d p e r p l a n t I l l x i Acknowledgements I would l i k e t o t h a n k Dr. M.K. Upadhyaya, my r e s e a r c h s u p e r v i s o r , f o r h i s g u i d a n c e and s u p p o r t t h r o u g h o u t t h e e n t i r e p r o j e c t . I a l s o w i s h t o t h a n k Mr. M. Sweeney f o r s u g g e s t i n g t h e t o p i c ; Dr. M. P i t t , Dr. G.W.E. E a t o n , and Ms. M. Qi f o r t h e i r d i s c u s s i o n s on s t a t i s t i c a l a n a l y s i s ; and Mr. M. W i e s s and Dr. S. S m i t h f o r t h e i r h e l p w i t h t h e s c a n n i n g e l e c t r o n m i c r o s c o p y . - 1 -1. Introduction Brassica oTeracea L. o r i g i n a l l y came from Europe. The w i l d p l a n t grows on t h e c h a l k s e a c l i f f s o f E n g l a n d , Denmark, n o r t h w e s t e r n F r a n c e and v a r i o u s a r e a s f r o m G r e e c e t o t h e U n i t e d Kingdom ( H e n s l o w 1912, S p l i t t s t o e s s e r 1979). I t i s a l e a f y , n o n h e a d i n g , p e r e n n i a l herb w i t h a r e l a t i v e l y l a r g e stem ( H e n s l o w 1 9 1 2 ) . Used o r i g i n a l l y as a g a r n i s h , s e l e c t i o n o f d i f f e r e n t w i l d forms produced t h e c u l t i v a r s we know t o d a y . Known c o l l e c t i v e l y as c o l e c r o p s t h e s e d i f f e r e n t c u l t i v a r s i n c l u d e b r o c c o l i , c a u l i f l o w e r , cabbage, B r u s s e l s s p r o u t s , k a l e , and k o h l r a b i . C o l e c r o p s a r e p l a n t e d i n rows and a r e grown as a n n u a l s . They r e q u i r e 60 t o 100 days t o a t t a i n a h a r v e s t a b l e s t a g e ( S p l i t t s t o e s s e r 1979). P a r t s h a r v e s t e d i n c l u d e undeveloped i n f l o r e s c e n c e s ( b r o c c o l i and c a u l i f l o w e r ) , l a r g e compressed buds ( B r u s s e l s s p r o u t s ) , o r c o m p r e s s e d l e a v e s ( c a b b a g e ) . S e e d l i n g s o f t h e s e p l a n t s emerge one t o t h r e e weeks a f t e r s o w i n g . F o r i n s t a n c e , c a u l i f l o w e r s e e d e d t o a d e p t h o f 1 cm r e q u i r e d 10 t o 20 d a y s t o emerge ( s o i l t e m p e r a t u r e was 15 and 10°C r e s p e c t i v e l y ) ( L o r e n z and Maynard 1 9 8 8 ) . Under t h e same c o n d i t i o n s cabbage t o o k 9 t o 15 days ( L o r e n z and Maynard 1988). B r o c c o l i r e q u i r e d 11, 16, and 22 days t o a c h i e v e 50 p e r c e n t emergence ( s o i l t e m p e r a t u r e s o f 13.4, 10.1, and 6.4°C r e s p e c t i v e l y ) ( H e g a r t y 1974). A f t e r emergence, i n i t i a l s e e d l i n g g r o w t h i s s l o w . R a p i d i n c r e a s e s i n d r y m a t t e r a c c u m u l a t i o n o c c u r l a t e r i n t h e g r o w i n g s e a s o n . B r o c c o l i p l a n t s , f o r example, t a k e 58 t o 76 days t o a t t a i n h a l f t h e i r d r y m a t t e r a c c u m u l a t i o n w h i l e 90 p e r c e n t d r y m a t t e r a c c u m u l a t i o n t a k e s 70 t o 95 days ( B e v e r l y e t a l . 1 986). -2-The r o o t s o f c o l e c r o p s a r e l o c a t e d i n t h e u p p e r 20 t o 30 cm o f s o i l ( Nieuwhof 1969). The p l a n t s grow t o an a p p r o x i m a t e h e i g h t o f 30 t o 90 cm. T h i s l i m i t e d s i z e as w e l l as t h e s l o w i n i t i a l emergence and g r o w t h and w i d e row s p a c i n g make c o l e c r o p s p o o r c o m p e t i t o r s a g a i n s t weeds. I n d e e d , t h e few s t u d i e s a v a i l a b l e s u g g e s t t h a t c o l e c r o p s r e q u i r e some f o r m o f weed c o n t r o l t o a v o i d y i e l d l o s s e s . A g a m a l i a n ( 1 9 7 6 ) , f o r i n s t a n c e , r e p o r t e d y i e l d r e d u c t i o n s i n b r o c c o l i when weeds grew w i t h t h e c r o p f o r l o n g e r t h a n 30 d a y s a f t e r c r o p g e r m i n a t i o n . However, a s i n g l e weeding 3 weeks a f t e r c r o p (cabbage) emergence was a l l t h a t was r e q u i r e d t o a v o i d y i e l d l o s s e s ( R o b e r t s e t a l . 1976, Weaver 1984). I n C a n a d a , weed c o n t r o l o p t i o n s f o r c o l e c r o p s i n c l u d e hand w e e d i n g , m e c h a n i c a l c u l t i v a t i o n , and two p r e - e m e r g e n c e h e r b i c i d e s ( t r i f l u r a l i n ( T r e f l a n ) and DCPA ( D a c t h a l ) ) . Each o p t i o n , however, has i t s l i m i t a t i o n s . Hand weeding, f o r i n s t a n c e , i s e x p e n s i v e , c o s t i n g B.C. f a r m e r s 225 d o l l a r s ha" 1 i n 1982 (B.CM.A.F. 1982). C u l t i v a t i o n does not c o n t r o l weeds w i t h i n t h e c r o p row. T r i f l u r a l i n o n l y w o rks w e l l i f t h e s o i l t e m p e r a t u r e i s above 15°C, not a common o c c u r r e n c e d u r i n g t h e c o o l wet s p r i n g s o f B r i t i s h C o l u m b i a . In a d d i t i o n , i t does n o t c o n t r o l s h e p h e r d ' s - p u r s e (Capsella bursa-pastoris), l a d y ' s - t h u m b (Polygonum persicaria), s m a r t w e e d (Polygonum scabrum), c u d w e e d (Gnaphalium uliginosum), o r t h e mustards (Sinapis s p p . ) . S i m i l a r l y , DCPA does not work w e l l i f t h e s o i l t e m p e r a t u r e i s below l S ' C and i t does not c o n t r o l many b r o a d l e a f s p e c i e s . In a d d i t i o n , both t r i f l u r a l i n and DCPA a r e not e f f e c t i v e on muck s o i l s o r m i n e r a l s o i l s w i t h a h i g h o r g a n i c m a t t e r c o n t e n t . -3-C o l e c r o p g r owers i n t h e U n i t e d S t a t e s were i n a s i m i l a r s i t u a t i o n when t h e y l o s t t h e r e g i s t r a t i o n f o r two i m p o r t a n t p o s t - e m e r g e n t h e r b i c i d e s , n i t r o f e n (Tok) and CDEC (Vegadex) ( N a e g e r l y 1985). However, p o s t - e m e r g e n t weed c o n t r o l i n o n i o n s o f f e r e d a p o s s i b l e s o l u t i o n . In t h e p a s t , g r o wers o f g r e e n d e h y d r a t e d o n i o n s had u s e d a p o s t - e m e r g e n t s p r a y o f s u l p h u r i c a c i d t o k i l l weeds ( N a e g e r l y 1985, Cudney and O r l o f f 1988). D i f f e r e n t i a l r e t e n t i o n on t h e f o l i a g e was t h e p r o p o s e d b a s i s o f s u l p h u r i c a c i d s e l e c t i v i t y : t h e waxy and u p r i g h t l e a v e s o f t h e o n i o n s r e p e l t h e s u l p h u r i c a c i d . However, s u l p h u r i c a c i d i s a dangerous c h e m i c a l . F u r t h e r m o r e , i t c o r r o d e s s p r a y equipment, l o w e r s s o i l pH, and c a u s e s c r o p damage under c e r t a i n c i r c u m s t a n c e s . These e f f e c t s prompted t h e development o f a s a f e r f o r m u l a t i o n c a l l e d N-pHURIC w h i c h i s a c o m b i n a t i o n o f s u l p h u r i c a c i d and l i q u i d u r e a . N-pHURIC i s l e s s dangerous t o work w i t h , i s l e s s c o r r o s i v e on t h e equipment, and i s l e s s l i k e l y t o burn t h e c r o p . I t a l s o c o n t r o l s t h e weeds as w e l l as t h e s u l p h u r i c a c i d a l o n e . C o l e c r o p s a l s o have a p r o m i n e n t c u t i c u l a r wax l a y e r on t h e i r stems and l e a v e s . T h e r e f o r e , d e s p e r a t e b r o c c o l i g r o w e r s have u s e d one f o r m u l a t i o n o f N-pHURIC c a l l e d N-TAC f o r p o s t - e m e r g e n t weed c o n t r o l . W h i l e t h e N-TAC i s l e s s dangerous and c o r r o s i v e t h a n t h e s u l p h u r i c a c i d a l o n e , i t s t i l l damages s p r a y equipment. S t u d i e s a t t h e U n i v e r s i t y o f C a l i f o r n i a f o u n d t h a t ammonium n i t r a t e (20-0-0) gave s i m i l a r r e s u l t s as N-TAC, but w i t h o u t e x c e s s i v e c o r r o s i v e n e s s ( A g a m a l i a n 1984). As a l i q u i d f e r t i l i z e r , ammonium n i t r a t e has some ad v a n t a g e s o v e r c o n v e n t i o n a l h e r b i c i d e s . F i r s t , i t s f e r t i l i z e r s t a t u s means t h a t -4-r e g i s t r a t i o n o f t h e p r o d u c t may be e a s y t o o b t a i n . T h i s i s v e r y i m p o r t a n t s i n c e t h e c u r r e n t e c o n o m i c s o f p r o d u c t d e v e l o p m e n t and r e g i s t r a t i o n make i t u n l i k e l y t h a t new c o m m e r c i a l p r o d u c t s w i l l be d e v e l o p e d f o r t h e l i m i t e d c o l e c r o p a c r e a g e . Second, i r r i g a t i o n two t o t h r e e days a f t e r ammonium n i t r a t e a p p l i c a t i o n washes t h e c h e m i c a l t o t h e r o o t s where i t can be u t i l i z e d as a n i t r o g e n s o u r c e ( A g a m a l i a n 1984). T h i r d , t h e m a t e r i a l i s r e l a t i v e l y s a f e t o w o r k w i t h , g i v i n g t h e a p p l i c a t o r freedom from cumbersome p r o t e c t i v e equipment. F o u r t h , i t i s e n v i r o n m e n t a l l y s a f e when used a p p r o p r i a t e l y . The l i m i t e d number o f s t u d i e s on weed i n t e r f e r e n c e i n c o l e c r o p s and t h e l a c k o f a p o s t - e m e r g e n t h e r b i c i d e p r o m p t e d t h e two g e n e r a l o b j e c t i v e s o f t h i s t h e s i s : ( 1 ) t o d e t e r m i n e t h e e f f e c t o f weed i n t e r f e r e n c e on c o l e c r o p s and (2) t o d e t e r m i n e t h e f e a s i b i l i t y o f u s i n g a p o s t - e m e r g e n t s p r a y o f l i q u i d ammonium n i t r a t e i n t h e l o w e r F r a s e r V a l l e y (B.C.) t o c o n t r o l weeds i n c o l e c r o p s . More s p e c i f i c a l l y t h e o b j e c t i v e s o f t h i s s t u d y w e r e t o d e t e r m i n e ( 1 ) t h e e f f e c t o f l a m b ' s - q u a r t e r s i n t e r f e r e n c e on t h e growth and y i e l d o f d i r e c t seeded b r o c c o l i , (2) t h e r e l a t i v e s u s c e p t i b i l i t y o f d i f f e r e n t weed s p e c i e s t o ammonium n i t r a t e , (3) t h e e f f e c t o f s h e p h e r d ' s - p u r s e d e n s i t y on weed c o n t r o l by ammonium n i t r a t e , ( 4 ) t h e r e l a t i v e s u s c e p t i b i l i t y o f d i f f e r e n t c o l e and o n i o n c u l t i v a r s t o ammonium n i t r a t e , and (5) t h e b a s i s o f ammonium n i t r a t e s e l e c t i v i t y . -5-2. L i t e r a t u r e Review 2.1 Weed I n t e r f e r e n c e When weed s p e c i e s compete w i t h c r o p p l a n t s f o r l i m i t e d r e s o u r c e s , t h e y i n t e r f e r e w i t h c r o p g r o w t h and y i e l d . R e s o u r c e s competed f o r i n c l u d e l i g h t , w a t e r , n u t r i e n t s , and C 0 2 , a l t h o u g h C 0 2 i s r a r e l y l i m i t i n g i n f i e l d s i t u a t i o n s . Weeds may a l s o i n t e r f e r e w i t h c r o p growth and y i e l d v i a a l l e l o p a t h y . ( i ) C o m p e t i t i o n f o r L i m i t e d R e s o u r c e s Light. P l a n t h e i g h t and c a n o p y d e v e l o p m e n t a r e o f p r i m a r y i m p o r t a n c e i n t h e c o m p e t i t i o n f o r l i g h t (Gaudet and Keddy 1988). L i g h t a v a i l a b i l i t y and q u a l i t y d e c r e a s e e x p o n e n t i a l l y w i t h d i s t a n c e below t h e t o p o f t h e canopy ( F i t t e r and Hay 1983). T h e r e f o r e , i f a weed has even a s m a l l advantage i n h e i g h t , i t can have a major n e g a t i v e e f f e c t on c r o p g r o w t h . F o r t h e same r e a s o n , development o f t h e c r o p canopy w h i c h can sh a d e o u t t h e weeds i s a m a j o r weed management s t r a t e g y ( P a t t e r s o n 1985). H e i g h t d i f f e r e n c e s o f v a r i o u s weed s p e c i e s have been l i n k e d t o d i f f e r e n c e s i n c o m p e t i t i v e a b i l i t y . F o r example, t a l l g r o w i n g s p e c i e s s u c h as l a m b ' s - q u a r t e r s (Chenopodium album) and dog n e t t l e (Urtica urens) c a u s e d a 91 t o 100 p e r c e n t r e d u c t i o n i n cabbage y i e l d ( R o b e r t s and Bond 1975, R o b e r t s e t a l . 1976). R e l a t i v e l y s h o r t e r s p e c i e s such as a m i x e d p o p u l a t i o n o f f u m i t o r y (Fumaria officinalis), b i r d ' s - e y e s p e e d w e l l {Veronica persica), a n n u a l b l u e g r a s s (Poa annua), and b l a c k n i g h t s h a d e {Solanum nigrum) o r a m i x e d p o p u l a t i o n o f b i r d ' s - e y e -6-s p e e d w e l l and b l a c k n i g h t s h a d e o n l y caused 47 and 25 p e r c e n t r e d u c t i o n s r e s p e c t i v e l y i n cabbage y i e l d ( R o b e r t s and Bond 1975, R o b e r t s e t a l . 1976). Weed c h a r a c t e r i s t i c s i m p o r t a n t i n c o n f e r r i n g a h e i g h t advantage o v e r t h e c r o p i n c l u d e e a r l y g e r m i n a t i o n and r a p i d e a r l y growth ( A l d r i c h 1 987). Indeed, t h e s e l e c t i v e p r e s s u r e s on weed s p e c i e s appear t o l e a d t o t h e development o f such c h a r a c t e r i s t i c s . F o r example, a co m p a r i s o n o f two p o o r j o e {Diodia feres) p o p u l a t i o n s , one weedy ( g r o w i n g w i t h soybean) t h e o t h e r nonweedy ( g r o w i n g i n t h e w i l d ) , r e v e a l e d t h a t t h e weedy p o p u l a t i o n had an e a r l i e r and g r e a t e r e s t a b l i s h m e n t r a t e and a g r e a t e r e a r l y above-ground growth r a t e ( J o r d e n 1989). Slow emergence has been l i n k e d t o t h e poor c o m p e t i t i v e a b i l i t y and d r a s t i c y i e l d r e d u c t i o n s o f o n i o n and g a r l i c (Hewson and R o b e r t s 1973, W i l l i a m a n d W a r r e n 1 9 7 5 ) . F i v e t o 59 p e r c e n t o f t h e f i n a l weed d e n s i t i e s o f a m i x e d p o p u l a t i o n [ p r o s t r a t e k n o t w e e d (Polygonum aviculare), c h i c k w e e d (Stellaria media), annual b l u e g r a s s , and f u m i t o r y ] emerged b e f o r e t h e o n i o n s (Hewson and R o b e r t s 1 9 7 3 ) . I n a d d i t i o n , maximum weed g r o w t h was l a r g e r and o c c u r r e d e a r l i e r t h a n c r o p growth (Hewson and R o b e r t s 1973). When t h e o n i o n c r o p began i t s e x p o n e n t i a l growth phase, t h e d r y w e i g h t o f t h e weeds p e r u n i t a r e a was a l r e a d y 20 t i m e s t h a t o f t h e c r o p (Hewson and R o b e r t s 1973). R a p i d g r o w t h was l i n k e d t o t h e s t r o n g c o m p e t i t i v e a b i l i t y o f l a m b ' s - q u a r t e r s i n d i r e c t s e e d e d cabbage ( R o b e r t s e t a l . 1 9 7 6 ) . The maximum f r e s h w e i g h t o f t h e l a m b ' s - q u a r t e r s o c c u r r e d 7 weeks a f t e r 50 p e r c e n t c r o p e m e r g e n c e w h i l e f o r t h e m i x e d p o p u l a t i o n ( f u m i t o r y , -7-b i r d ' s - e y e s p e e d w e l l , a n n u a l b l u e g r a s s , and b l a c k n i g h t s h a d e ) i t o c c u r r e d 12 weeks a f t e r 50 p e r c e n t c r o p emergence ( R o b e r t s e t a l . 1976). The i m p o r t a n c e o f e a r l y , r a p i d growth can a l s o be seen i n a s t u d y o f weed c o m p e t i t i o n i n f a l l t r a n s p l a n t e d c a b b a g e ( L a w s o n 1 9 7 2 ) . C h i c k w e e d , an o t h e r w i s e l o w - g r o w i n g , n o n c o m p e t i t i v e weed, began g r o w t h e a r l y i n t h e s p r i n g and g r e w so r a p i d l y t h a t i t c o v e r e d a l l t h e a v a i l a b l e g r o u n d . In t h e p r o c e s s , t h e c h i c k w e e d d o m i n a t e d t h e weed f l o r a and shaded t h e c r o p by g r o w i n g o v e r i t . Crop l o s s e s were 18, 25, and 51 p e r c e n t i n t h r e e d i f f e r e n t y e a r s . Nutrients and Water. P l a n t r o o t d e n s i t y , l e n g t h , o r d e p t h a r e i m p o r t a n t i n t h e c o m p e t i t i o n f o r w a t e r and n u t r i e n t s (Gaudet and Keddy 1988). F o r example, o n i o n p l a n t s grown w i t h weeds had f e w e r r o o t s t h a n t h o s e grown w i t h o u t weeds and c o n s e q u e n t l y t o o k up l e s s N, P, and K (Hewson and R o b e r t s 1973). The o n i o n s grown w i t h t h e weeds c o n s i s t e n t l y had a l o w e r N c o n t e n t t h a n t h e w e e d - f r e e o n i o n s and, t h e r e f o r e , Hewson and R o b e r t s (1973) s u g g e s t e d t h a t c o m p e t i t i o n may i n i t i a l l y have been f o r N, a l t h o u g h w a t e r may have been l i m i t i n g and c r o p s h a d i n g may a l s o have confounded n u t r i e n t e f f e c t s . R e g a r d l e s s o f t h e r e s o u r c e t h a t f i r s t becomes l i m i t e d , r e d u c e d g r o w t h o f e i t h e r t h e s h o o t s o r r o o t s w i l l r e s u l t i n r e d u c e d growth o f b o t h (Keddy and S h i p l e y 1 9 8 9 ) . H e n c e , i f a weed g a i n s an i n i t i a l a d v antage o v e r t h e c r o p , a n e g a t i v e f e e d b a c k r e s u l t s and c r o p growth and y i e l d i s r e d u c e d . -8-(ii) Allelopathy A l l e l o p a t h y r e f e r s t o t h e b i o c h e m i c a l i n t e r a c t i o n s ( i n h i b i t o r y o r s t i m u l a t o r y ) between p l a n t s . P l a n t s p e c i e s may r e l e a s e i n h i b i t o r y b i o c h e m i c a l s t h a t r e d u c e emergence, g r o w t h and y i e l d , r e s i s t a n c e t o p l a n t pathogens i n o t h e r s p e c i e s as w e l l as n o d u l a t i o n and N - f i x a t i o n i n legumes ( R i c e 1 9 7 4 ) . F o r example, when q u a c k g r a s s [Agropyron repens) was grown w i t h snapbeans (Phaseolus vulgaris), navybeans (P. vulgaris), and s o y b e a n s [Glycine max) t h e s h o o t w e i g h t , r o o t w e i g h t , and r o o t n o d u l a t i o n o f t h e legumes was s i g n i f i c a n t l y d e c r e a s e d (Weston and Putnam 1985). (iii) Shifting the Balance The d e g r e e t o w h i c h a weed s p e c i e s competes w i t h a c r o p i s n o t f i x e d , b u t c h a n g e s d e p e n d i n g on e n v i r o n m e n t a l c o n d i t i o n s and t h e p r e s e n c e o r absence o f pathogens and i n s e c t p e s t s . Environment. T e m p e r a t u r e , s o i l m o i s t u r e , l i g h t ( i n t e n s i t y , s p e c t r a l c o m p o s i t i o n , and p e r i o d i c i t y ) and 0 2 a v a i l a b i l i t y d e t e r m i n e i f a seed w i l l g e r m i n a t e . Weed s e e d s t h a t g e r m i n a t e t e n d t o be l o c a t e d c l o s e t o t h e s o i l s u r f a c e compared t o t h e p l a n t i n g d e p t h o f c r o p seeds ( A l d r i c h 1987). T h e r e f o r e , d e p e n d i n g on t h e e n v i r o n m e n t a l c o n d i t i o n s , e s p e c i a l l y s o i l t e m p e r a t u r e and m o i s t u r e , weed seeds c l o s e t o t h e s o i l s u r f a c e may emerge s o o n e r o r l a t e r t h a n t h e c r o p ( A l d r i c h 1987). S m a l l d i f f e r e n c e s i n r e l a t i v e t i m e s o f emergence can have a l a r g e e f f e c t on t h e outcome o f i n t e r s p e c i f i c c o m p e t i t i o n . F o r e x a m p l e , -9-v a r i a t i o n s i n t h e c o m p e t i t i v e a b i l i t y o f w h i t e m u s t a r d (Brassica hirta) grown w i t h peas (Pisum sativum) was i n p a r t a t t r i b u t e d t o d i f f e r e n c e s i n r e l a t i v e emergence ( N e l s o n and Nylund 1962). The weed competed b e t t e r when s o i l m o i s t u r e was h i g h because t h i s p e r m i t t e d t h e w h i t e mustard t o emerge t h r e e days b e f o r e t h e c r o p ( N e l s o n and N y l u n d 1 9 6 2 ) . However, u n d e r d r y c o n d i t i o n s t h e weed emerged f o u r d a y s a f t e r t h e c r o p and c o n s e q u e n t l y c r o p y i e l d was g r e a t l y improved ( N e l s o n and N y l u n d 1962). D i f f e r e n c e s i n t e m p e r a t u r e and s o i l m o i s t u r e may a l s o i n f l u e n c e p l a n t c o m p e t i t i o n d e p e n d i n g on whether t h e p l a n t s p e c i e s a r e C 4 o r C 3. C 4 p l a n t s have h i g h e r p h o t o s y n t h e t i c r a t e s and use l e s s w a t e r under h o t , d r y c o n d i t i o n s t h a n C 3 p l a n t s and, t h e r e f o r e , t h e y compete b e t t e r under t h e s e c o n d i t i o n s ( P a t t e r s o n 1985). F o r example, when l a m b ' s - q u a r t e r s (a C 3 p l a n t ) was grown w i t h r e d r o o t pigweed {Amaranthus retroflexus) (a C 4 p l a n t ) a t a d a y / n i g h t t e m p e r a t u r e o f 24/18°C i t c o u l d compete as w e l l as th e r e d r o o t pigweed (Chu e t a l . 1978). However, i f t h e t e m p e r a t u r e was i n c r e a s e d t o 29/24°C t h e r e d r o o t pigweed dominated (Chu e t a l . 1978). S i m i l a r l y , a complex o f r e d r o o t pigweed and smooth pigweed {A. hybridus) i n c o t t o n competed much b e t t e r f o r w a t e r i n a d r y y e a r t h a n i t d i d i n a wet y e a r ( S t r e e t e t a l . 1985). S o i l pH i s a n o t h e r e n v i r o n m e n t a l f a c t o r t h a t may d e t e r m i n e t h e deg r e e t o whi c h two s p e c i e s compete. P o w e l l amaranth {A. powellii) and v e l v e t l e a f {Abutilon theophrasti) w e r e 50 a n d 67 p e r c e n t more c o m p e t i t i v e r e s p e c t i v e l y t h a n c o r n a t pH 6.0 t h a n a t pH 4.8 (Weaver and H a m i l l 1985). Green f o x t a i l was e q u a l l y c o m p e t i t i v e w i t h c o r n a t both pHs (Weaver and H a m i l l 1985). In a n o t h e r i n s t a n c e , s o i l pH c o m p l e t e l y -10-r e v e r s e d t h e c o m p e t i t i v e i n t e r a c t i o n o f o a t s and b a r l e y ( S i l v e r t o w n 1982). A t pH 6.4 b a r l e y was more c o m p e t i t i v e and had l a r g e r y i e l d s t h a n o a t s ( S i l v e r t o w n 1982). A t pH 3.7, o a t s became more c o m p e t i t i v e , w h i l e b a r l e y y i e l d s were d e p r e s s e d ( S i l v e r t o w n 1982). Pathoaen and Insect Pests. P l a n t - p l a n t i n t e r a c t i o n s a r e c o m p l i c a t e d by pathogen and i n s e c t p e s t s . D i s e a s e and i n s e c t s can have a c o n s i d e r a b l e i m p a c t on t h e a g g r e s s i v e n e s s o f t h e h o s t s p e c i e s and, hence, t h e f i n a l outcome o f i n t e r s p e c i f i c c o m p e t i t i o n . F o r example, i n a b a r l e y - w h e a t m i x t u r e a b a r l e y p a t h o g e n g r e a t l y r e d u c e d t h e c o m p e t i t i v e n e s s o f b a r l e y ( B u r d a n and C h i l v e r s 1 9 7 7 ) . I n a n o t h e r i n s t a n c e , c r o w n r u s t on r y e g r a s s i n a r y e g r a s s - w h i t e c l o v e r m i x t u r e r e d u c e d r y e g r a s s y i e l d s by 84 p e r c e n t , w h i l e w h i t e c l o v e r y i e l d i n c r e a s e d by 87 p e r c e n t ( L a t c h and L a n c a s h i r e 1970). ( i v ) S t u d y i n g Weed I n t e r f e r e n c e Many e x p e r i m e n t a l m e t h o d o l o g i e s have been d e v e l o p e d t o s t u d y t h e e f f e c t s o f weed i n t e r f e r e n c e on p l a n t growth and y i e l d . A p p r o a c h e s used f a l l i n t o f o u r e x p e r i m e n t a l t y p e s : ( 1 ) a d d i t i v e , ( 2 ) s u b s t i t u t i v e , ( 3 ) s y s t e m a t i c , and (4) n e i g h b o u r h o o d and a l l have been r e v i e w e d by R a d o s e v i c h ( 1 9 8 7 ) . O f t e n t h e o b j e c t i v e s o f such s t u d i e s a r e t o p r o v i d e g r o wers w i t h a s a t i s f a c t o r y way t o r e l a t e l e v e l s o f weed i n f e s t a t i o n t o r e d u c t i o n s i n y i e l d so t h e y can d e c i d e when weed c o n t r o l i s e c o n o m i c a l and w a r r a n t e d ( A l d r i c h 1987). The most common e x p e r i m e n t a l d e s i g n used t o s t u d y weed-crop c o m p e t i t i o n i s t h e a d d i t i v e s e r i e s ( R a d o s e v i c h 1987). -11-The use o f a d d i t i v e s e r i e s and s i m p l e m a t h e m a t i c a l models can be used t o p r e d i c t y i e l d l o s s e s due t o weeds o v e r a w i d e r a n g e o f c r o p p i n g s i t u a t i o n s ( P o o l e and G i l l 1987) Additive Series Experiments. In a d d i t i v e s e r i e s e x p e r i m e n t s two s p e c i e s a r e grown t o g e t h e r w i t h t h e d e n s i t y o f one, u s u a l l y t h e c r o p , h e l d c o n s t a n t and t h e o t h e r , u s u a l l y t h e weed, v a r y i n g . T h i s t y p e o f e x p e r i m e n t a p p r o x i m a t e s t h e farm s i t u a t i o n where c r o p d e n s i t y i s s e t by t h e f a r m e r and weeds a r e v a r i a b l e . The y i e l d d a t a g e n e r a t e d from a d d i t i v e e x p e r i m e n t s u s u a l l y has a h y p e r b o l i c shape (Cousens 1987, P o o l e and G i l l 1 9 8 7 ) . T r a d i t i o n a l l y , however, m u l t i p l e c o m p a r i s o n t e s t s ( e g . Duncan's m u l t i p l e range t e s t o r l e a s t s i g n i f i c a n t d i f f e r e n c e ) w ere u s e d t o a n a l y s e c r o p y i e l d - w e e d d e n s i t y d a t a . T h i s t y p e o f a n a l y t i c a l a p p r o a c h u s u a l l y f i n d s c r o p y i e l d s a t low weed d e n s i t i e s t o be i n s i g n i f i c a n t l y d i f f e r e n t f r o m t h e w e e d - f r e e c o n t r o l s . S u c h r e s u l t s l e d t o t h e b e l i e f t h a t t h e r e l a t i o n s h i p b e t w e e n i n c r e a s i n g weed d e n s i t y and c r o p y i e l d was s i g m o i d a l ( C o u s e n s 1 9 8 7 ) . H o w e v e r , C o u s e n s ( 1 9 8 5 ) ha s r e c e n t l y d e v e l o p e d a r e c t a n g u l a r h y p e r b o l a t h a t was r e p e a t e d l y f o u n d t o be a good model f o r c r o p y i e l d - w e e d d e n s i t y d a t a . The most i n t e r e s t i n g f e a t u r e o f t h e h y p e r b o l i c model i s t h e l a r g e y i e l d l o s s e s a t l o w weed d e n s i t i e s , w h i c h i s o f t e n t h e a r e a o f c o m m e r c i a l i n t e r e s t . A l t h o u g h i t i s p o s s i b l e t h a t a h y p o t h e t i c a l s i t u a t i o n o f u n l i m i t e d r e s o u r c e s c o u l d e x i s t where t h e " f i r s t " weed would n o t e f f e c t c r o p y i e l d , t h i s s i t u a t i o n r a r e l y o c c u r s i n t h e f i e l d -12-( P o o l e and G i l l 1987). From c o m p a r i s i o n s o f c r o p g r o w t h i n weedy and w e e d - f r e e p l o t s m o n i t o r e d o v e r t i m e , t h e t i m e when t h e weeds b e g i n t o l i m i t c r o p growth can be d e t e r m i n e d . T h i s t i m e i s known as t h e o n s e t o f weed c o m p e t i t i o n . M u l t i p l e c o m p a r i s o n t e s t s have a l s o been used i n a p p r o p r i a t e l y t o d e t e r m i n e t h e o n s e t o f weed c o m p e t i t i o n (Cousens 1 9 8 8 ) . T r a d i t i o n a l a n a l y s i s has o v e r e s t i m a t e d t h e t i m e a t w h i c h weeds b e g i n t o i n t e r f e r e w i t h c r o p g r o w t h (Cousens 1 9 8 8 ) . An a l t e r n a t i v e a n a l y s i s i s t o l o g t r a n s f o r m t h e d a t a t o o b t a i n a homogeneous v a r i a n c e , p l o t t h e d a t a t o i n d i c a t e a r e l e v a n t m o d e l , and t h e n f i t t h e t r a n s f o r m e d d a t a by r e g r e s s i o n . Such an a n a l y s i s i s more l i k e l y t o g i v e a b e t t e r e s t i m a t i o n o f t h e t i m e o f o n s e t o f weed c o m p e t i t i o n (Cousens 1988). 2.2 Weed C o n t r o l S t r a t e g i e s Weed c o n t r o l s t r a t e g i e s f a l l i n t o t h r e e m a i n c a t e g o r i e s : ( 1 ) e r a d i c a t i o n , ( 2 ) p r o p h y l a x i s , and ( 3 ) c o n t a i n m e n t ( C o u s e n s 1 9 8 7 ) . E r a d i c a t i o n o r c o m p l e t e e l i m i n a t i o n o f a weed s p e c i e s i s o f t e n i m p o s s i b l e and c o s t l y , a l t h o u g h weed numbers may be r e d u c e d t o l e v e l s t h a t a r e o f l i t t l e consequence. However, when a weed s p e c i e s i s newly i n t r o d u c e d and c o n f i n e d t o a s m a l l a r e a t h e n e r a d i c a t i o n i s o f t e n w o r t h w h i l e and e f f e c t i v e . P r o p h y l a x i s does not a t t e m p t t o e l i m i n a t e a l l weeds, but i n v o l v e s a c h i e v i n g a l e v e l o f weed c o n t r o l t h a t a v o i d s o r m i n i m i z e s t h e l o s s o f r e v e n u e . T h i s s t r a t e g y u t i l i z e s r e g u l a r s c h e d u l e d a p p l i c a t i o n s o f h e r b i c i d e s . T h e r e f o r e , i t t e n d s t o be e x c e s s i v e and w a s t e f u l o f -13-c h e m i c a l s , may be h a r m f u l t o t h e e n v i r o n m e n t , and l e n d s i t s e l f t o t h e d e v e l o p m e n t o f r e s i s t a n t weeds ( e g . t r i a z i n e - r e s i s t a n t weeds; De Prado e t a l . 1989). C o n t a i n m e n t t r i e s t o keep t h e weed p o p u l a t i o n b e l o w a s p e c i f i c l e v e l t h a t w i l l , i n p r i n c i p l e , r e s u l t i n weed c o n t r o l o n l y when i t i s j u s t i f i e d . A c o n t a i n m e n t s t r a t e g y , t h e r e f o r e , r e l i e s on d e t e r m i n i n g an a p p r o p r i a t e weed p o p u l a t i o n l e v e l o r t h r e s h o l d a t w h i c h t h e weeds s h o u l d be c o n t r o l l e d and t h e m o n i t o r i n g o f weed p o p u l a t i o n s i n t h e f i e l d . A t p r e s e n t a c o n t a i n m e n t s t r a t e g y i s d i f f i c u l t t o implement. A m u l t i t u d e o f d i f f e r e n t t h r e s h o l d d e f i n i t i o n s e x i s t and c a l c u l a t i o n s o f t h r e s h o l d l e v e l s a r e o f t e n n a i v e and do n o t make economic s e n s e ( C o u s e n s 1 9 8 7 ) . I f c o n t a i n m e n t i s t o become a v i a b l e a l t e r n a t i v e l e s s emphasis must be l a i d on t h r e s h o l d l e v e l s and much more on b a s i c i n f o r m a t i o n a b o u t c o m p e t i t i o n , p o p u l a t i o n d y n a m i c s , and h e r b i c i d e p e r f o r m a n c e ( C o u s e n s 1987). The f i n a n c i a l a d v a n t a g e s o f a c o n t a i n m e n t weed c o n t r o l s t r a t e g y v e r s e s a p r o p h y l a x i s weed c o n t r o l s t r a t e g y a r e a t p r e s e n t s m a l l (Cousens 1 9 8 7 ) . Hence, i t s h o u l d come as no s u r p r i s e t h a t p r o p h y l a x i s i s t h e s t r a t e g y u s e d t o c o n t r o l weeds i n c o l e c r o p s . The p r e - e m e r g e n t h e r b i c i d e , t r i f l u r a l i n , i s t h e o n l y e f f e c t i v e h e r b i c i d e a v a i l a b l e i n B.C. (Sweeney 1 9 8 2 ) . Such a p r e - e m e r g e n t t r e a t m e n t i s p r o p h y l a c t i c b e c a u s e i t m u s t be a p p l i e d b e f o r e a n y w e e d s h a v e e m e r g e d . U n f o r t u n a t e l y , t h e r e p e a t e d u s e o f t h i s c h e m i c a l h a s r e s u l t e d i n r e s i s t a n t weed p o p u l a t i o n s (Sweeney 1982). T h e r e f o r e , p r o d u c e r s have had t o r e l y on t i m e l y p o s t - e m e r g e n t c u l t i v a t i o n and hand w e e d i n g t o c o n t r o l r e s i s t a n t weeds (Sweeney 1982). Hand weeding, not o n l y r e d u c e s c r o p s t a n d but i s a l s o r e l a t i v e l y e x p e n s i v e ( N a e g e r l y 1985). T h e r e f o r e , -14-t h e development o f a l t e r n a t i v e p o s t - e m e r g e nt weed c o n t r o l o p t i o n s would be d e s i r a b l e f o r B.C. g r o w e r s . 2.3 Post-emergent Meed Control in Cole Crops and Onion With Nitrogen Fertilizers In C a l i f o r n i a , a n o v e l post-emergent weed c o n t r o l method has been d e v e l o p e d . I t i n v o l v e s t h e use o f l i q u i d n i t r o g e n f e r t i l i z e r s t o c o n t r o l weeds i n c o l e c r o p s and o n i o n . L i q u i d f e r t i l i z e r s a c t as c o n t a c t h e r b i c i d e s . S u s c e p t i b l e weeds a r e k i l l e d w i t h i n 4 t o 6 h o u r s a f t e r a p p l i c a t i o n ( A g a m a l i a n 1 9 8 4 ) . The b a s i s o f c r o p t o l e r a n c e i s b e l i e v e d t o be a "good waxy c u t i c l e " on t h e l e a v e s and stem ( A g a m a l i a n 1 9 8 4 , N a e g e r l y 1 9 8 5 ) w h i c h e n a b l e s t h em t o r e p e l t h e f e r t i l i z e r s o l u t i o n s . A g a m a l i a n (1988) n o t e s t h a t " s e v e r a l weeds w i t h waxy l e a f s u r f a c e s t o l e r a t e d [ t h e ] ammonium n i t r a t e " . W h i l e wax has n o t been e x p e r i m e n t a l l y p r o v e n t o be t h e b a s i s o f ammonium n i t r a t e s e l e c t i v i t y , i t i s f a i r l y s a f e t o assume t h a t d i f f e r e n c e s i n s o l u t i o n r e t e n t i o n a r e i m p o r t a n t . The p r i m a r y p l a n t c h a r a c t e r i s t i c a f f e c t i n g r e t e n t i o n i s l e a f w e t t a b i l i t y , a l t h o u g h l e a f m o t i o n , o r i e n t a t i o n , s i z e , and shape a l s o p l a y m i n o r r o l e s ( H a i n e s e t a l . 1985, K i r k w o o d 1987). L e a f w e t t a b i l i t y i s o f t e n d e t e r m i n e d b y m e a s u r i n g a l e a f ' s s o l u t i o n h o l d i n g c a p a c i t y and/or a d v a n c i n g c o n t a c t a n g l e . S o l u t i o n h o l d i n g c a p a c i t y i s t h e amount o f s o l u t i o n r e t a i n e d p e r l e a f a r e a when a s o l u t i o n i s s p r a y e d on t h e whole p l a n t ( H a i n e s e t a l . 1985). A c o n t a c t a n g l e i s t h e a n g l e between t h e s u r f a c e o f t h e l e a f and t h e t a n g e n t p l a n e o f a d r o p l e t a t t h e c i r c l e o f c o n t a c t between a i r , l i q u i d , and l e a f when a known amount o f s o l u t i o n -15-i s p l a c e d on a f r e s h l y d e t a c h e d , h o r i z o n t a l l e a f p i e c e ( M a r t i n and J u n i p e r 1970, Haines e t a l . 1985). A c o n t a c t a n g l e o f 0° i n d i c a t e s a c o m p l e t e l y w e t t a b l e s u r f a c e ( i n p r a c t i c e n e v e r o b t a i n e d ) , w h i l e 180° i n d i c a t e s a t o t a l l y u n w e t t a b l e s u r f a c e , w i t h v a l u e s i n b e t w e e n i n d i c a t i n g v a r y i n g d e g r e e s o f w e t t a b i l i t y ( M a r t i n and J u n i p e r 1 9 7 0 ) . The magnitude o f t h e c o n t a c t a n g l e (when d r o p l e t s i z e and c h e m i s t r y i s c o n s t a n t ) i s l a r g e l y d e t e r m i n e d by t h e p h y s i c a l and c h e m i c a l n a t u r e o f t h e l e a f s u r f a c e . Surface chemistrv. The p r e s e n c e o r a b s e n c e o f wax l a r g e l y d e t e r m i n e s t h e c h e m i s t r y o f t h e l e a f s u r f a c e . The c u t i c l e i s h y d r o p h i l i c and i s e a s i l y w e t t e d by p o l a r s o l u t i o n s s u c h as w a t e r ( H o l l o w a y 1 9 7 0 ) . Wax, on t h e o t h e r hand, i s h y d r o p h o b i c and i s n o t e a s i l y w e t t e d by p o l a r s u b s t a n c e s ( H o l l o w a y 1970, Had l e y 1989). The more s p a r s e l y d i s t r i b u t e d t h e wax, t h e more t h e c u t i c l e i s exposed and, t h e r e f o r e , t h e more w e t t a b l e t h e s u r f a c e ( H o l l o w a y 1970). W h i l e t h e p r e s e n c e o r ab s e n c e o f wax can g r e a t l y i n f l u e n c e l e a f w e t t a b i l i t y , t h e c o n t a c t a n g l e s o f s m o o t h f i l m s o f m a j o r wax c o n s t i t u e n t s i n d i c a t e t h a t t h e y do not v a r y g r e a t l y i n t h e i r h y d r o p h o b i c p r o p e r t i e s ( H o l l o w a y 1 9 6 9 ) . F o r e x a m p l e , i n p e a s , a l k a n e s have a c o n t a c t a n g l e o f 108° and p r i m a r y a l c o h o l s have a c o n t a c t a n g l e o f 95°, a d i f f e r e n c e o f o n l y 13° ( H o l l o w a y 1969). Many l e a v e s , however, have much l a r g e r c o n t a c t a n g l e s than t h o s e p r o v i d e d by j u s t t h e h y d r o p h o b i c n a t u r e o f t h e w a x e s . S u r f a c e r o u g h n e s s e x p l a i n s any a d d i t i o n a l i n c r e a s e s i n c o n t a c t a n g l e s . -16-Surface roughness. S u r f a c e r o u g h n e s s c h a n g e s t h e " t r u e " c o n t a c t a n g l e by p r e v e n t i n g t h e d r o p l e t from making c o m p l e t e c o n t a c t w i t h t h e l e a f s u r f a c e , t h e r e b y d e c r e a s i n g t h e d r o p l e t / s u r f a c e i n t e r f a c e and i n c r e a s i n g t h e d r o p l e t / a i r i n t e r f a c e ( M a r t i n and J u n i p e r 1970). As t h e d r o p l e t / a i r i n t e r f a c e i n c r e a s e s so d o e s t h e c o n t a c t a n g l e and l e a f w e t t a b i l i t y d e c r e a s e s ( H o l l o w a y 1970). Indeed, any s u r f a c e i s h i g h l y u n w e t t a b l e p r o v i d e d t h a t t h e p r o j e c t i o n s f r o m i t a r e s m a l l e n o u g h , a l m o s t r e g a r d l e s s o f t h e c o m p o s i t i o n o f t h e p r o j e c t i o n s ( M a r t i n and J u n i p e r 1970). F o r example, c a r b o n i s not v e r y h y d r o p h o b i c , y e t i n t h e f o r m o f v e r y f i n e p a r t i c l e s on a s u r f a c e i t i s h i g h l y w a t e r r e p e l l e n t ( H a r t l e y and B u r n s k i l l 1958). L e a f r o u g h n e s s i s d e t e r m i n e d by l e a f v e n a t i o n , e p i d e r m a l c e l l s , t r i c h o m e s , and c r y s t a l l i n e wax s t r u c t u r e s ( H o l l o w a y 1 9 7 0 ) . P r o m i n e n t l e a f v e n a t i o n i n c r e a s e s l e a f r o u g h n e s s and v a r i e s w i t h d i f f e r e n t t a x o n o m i c g r o u p s . G e n e r a l l y , more x e r o m o r p h i c p l a n t s h a v e l e s s c o n s p i c u o u s v e i n s . Many m o n o c o t y l e d o n o u s p l a n t s h a ve a s e r i e s o f p r o m i n e n t v e i n - r i d g e s w h i c h run p a r a l l e l t o each o t h e r a l o n g t h e l e n g t h o f t h e l e a f . D i c o t y l e d o n s , on t h e o t h e r h a n d , have a r e t i c u l a t e v e n a t i o n , t h a t i s o n l y pronounced on t h e u n d e r s i d e o f t h e l e a v e s , t h e t o p s i d e h a v i n g t h e c u t i c l e s l i g h t l y d e p r e s s e d a l o n g t h e l e a f v e i n s ( H o l l o w a y 1970). E p i d e r m a l c e l l s c a n i n f l u e n c e l e a f r o u g h n e s s by t h e i r v a r y i n g shapes and s i z e s as w e l l as t h e i r s u r f a c e morphology w h i c h may be f l a t , c o n v e x , o r p a p i l l o s e ( b e a r i n g a s m a l l c o n i c a l s t r u c t u r e ) ( H o l l o w a y 1970, M a r t i n and J u n i p e r 1 9 7 0 ) . In g e n e r a l p a p i l l o s e and c o n v e x s u r f a c e s c o n f e r g r e a t e r roughness t o l e a f s u r f a c e s t h e n do f l a t s u r f a c e s -17-( H o l l o w a y 1970). I f p a p i l l o s e o r convex c e l l s a r e p r e s e n t , t h e i r s i z e w i l l a l s o i n f l u e n c e c o r r u g a t i o n ( M a r t i n and J u n i p e r 1970). T r i c h o m e s a r e h a i r - l i k e o u t g r o w t h s o f e p i d e r m a l c e l l s . T h e y r o u g h e n t h e s u r f a c e and v a r y i n s i z e , s h a p e , t y p e , f r e q u e n c y , and d i s t r i b u t i o n b e t w e e n s p e c i e s and r e g i o n s o f t h e p l a n t . A l t h o u g h t r i c h o m e s r o u g h e n t h e s u r f a c e , i f a r r a n g e d i n a u n i f o r m o r 'open' p a t t e r n t h e y w i l l enhance l e a f w e t t i n g t h r o u g h c a p i l l a r y a c t i o n ( C h a l l e n 1 9 6 2 ) . On t h e o t h e r h a n d , i f p r e s e n t i n an i r r e g u l a r o r ' c l o s e d ' p a t t e r n t h e y a r e h i g h l y w a t e r r e p e l l e n t ( C h a l l e n 1962). The d e n s i t y o f t h e t r i c h o m e s a r r a n g e d i n t h e ' c l o s e d ' p a t t e r n s a l s o i n f l u e n c e s t h e w e t t a b i l i t y o f t h e l e a f ; l e a v e s w i t h l o w t r i c h o m e d e n s i t i e s p o s s e s s f e w e r a i r p o c k e t s so t h e i r s u r f a c e s a r e more e a s i l y w e t t e d ( C h a l l e n 1962). Wax m o r p h o l o g y c a n a l s o i n f l u e n c e l e a f r o u g h n e s s ; u p r i g h t s t r u c t u r e s s u c h as r o d l e t s , r i b b o n s , f i l a m e n t s , and t u b u l e s c r e a t e a bumpier l e a f s u r f a c e t h e n smooth f i l m s . Wax c o n s t i t u e n t s d e t e r m i n e t h e above wax morphology. F o r e x a m p l e , h y d r o - 0 - d i k e t o n e s and ^ - d i k e t o n e s p roduce t u b e s , n-ketones produce s p i k y p l a t e s , and n - s e c o n d a r y a l c o h o l s p r o d u c e p l a t e s ( s y m m e t r i c a l ) and t u b e s ( a s y m m e t r i c a l ) ( J u n i p e r and J e f f r e e 1 9 8 3 ) . P l a n t w axes a r e , h o w e v e r , made up o f d i f f e r e n t c o n s t i t u e n t s and, t h e r e f o r e , wax morphology w i l l v a r y d e p e n d i n g on t h e m i x t u r e and p r o p o r t i o n o f c o n s t i t u e n t s p r e s e n t . Based on t h e i r p h y s i c a l and c h e m i c a l p r o p e r t i e s , l e a f s u r f a c e s can be d i v i d e d i n t o t h r e e c a t e g o r i e s ( H o l l o w a y 1969). F i r s t , t h e r e a r e l e a f s u r f a c e s w i t h c o n t a c t a n g l e s l e s s t h a n 90° where t h e s u r f a c e roughness -18-h a s l i t t l e s i g n i f i c a n c e a n d wax i s n o t a p r e d o m i n a n t f e a t u r e ( i n c o m p l e t e l y c o v e r s t h e s u r f a c e e x p o s i n g t h e l e s s h y d r o p h o b i c c u t i c l e ) . S e c o n d , t h e r e a r e s u r f a c e s w i t h c o n t a c t a n g l e s between 90° and 110° w h e r e a smooth l a y e r o f wax e x i s t s o r c u t i c u l a r r o u g h n e s s p l a y s a moderate r o l e . T h i r d , t h e r e a r e s u r f a c e s w i t h c o n t a c t a n g l e s g r e a t e r t h a n 110° where a c r y s t a l l i n e wax u l t r a s t r u c t u r e c o m p l e t e l y c o v e r s t h e e n t i r e l e a f s u r f a c e o b s c u r i n g o t h e r c u t i c u l a r f e a t u r e s , o r c u t i c u l a r r o ughness i s v e r y e x t e n s i v e . The t h i r d l e a f s u r f a c e t y p e can be f u r t h e r c l a s s i f i e d i n t o t h o s e w i t h c o n t a c t a n g l e s between 110° and 140° and t h o s e g r e a t e r t h a n 140" ( M a r t i n and J u n i p e r 1970). S u r f a c e s w i t h c o n t a c t a n g l e s between 110° and 140° i n d i c a t e t h a t t h e d r o p l e t i s making p a r t i a l c o n t a c t w i t h t h e l e a f c u t i c l e . Those g r e a t e r t h a n 140" i n d i c a t e t h a t t h e d r o p l e t i s o n l y m a k i n g c o n t a c t w i t h t h e e p i c u t i c u l a r c r y s t a l l i n e wax. I f t h e l e a f s u r f a c e f a l l s i n t o t h i s l a s t c a t e g o r y t h e n a d r o p l e t w i l l be c o m p l e t e l y r e f l e c t e d f r o m t h e s u r f a c e , u n l e s s t h e s u r f a c e t e n s i o n o f t h e d r op i s l e s s t h a n 40 dyne cm - 1. L e a f w e t t a b i l i t y , h o w e v e r , i s n o t f i x e d a n d c h a n g e s w i t h e n v i r o n m e n t a l c o n d i t i o n s and p l a n t age w h i c h i n f l u e n c e t h e amount and t y p e o f e p i c u t i c u l a r wax p r o d u c e d . The Influence of Environment on Epicuticular Wax. I t i s t h e o r i z e d t h a t p l a n t s h a ve e v o l v e d c u t i c u l a r and e p i c u t i c u l a r waxes t o h e l p p r e v e n t and r e d u c e t r a n s p i r a t i o n a l l o s s e s ( H a d l e y 1989). There a r e two ways t h a t waxes can d e c r e a s e c u t i c u l a r t r a n s p i r a t i o n . F i r s t t h e i r h y d r o p h o b i c n a t u r e make them a n a t u r a l b a r r i e r t o w a t e r ( H a d l e y 1989). -19-Second, when t h e waxes a r e p r e s e n t on t h e l e a f s u r f a c e as p e r p e n d i c u l a r p r o j e c t i o n s , t h e y r e f l e c t o r s c a t t e r l i g h t away from t h e l e a f , t h e r e b y h e l p i n g t o l o w e r l e a f t e m p e r a t u r e ( J e f f e r s o n e t a l . 1989). B e c a u s e waxes a p p e a r t o be an a d a p t a t i o n f o r d e c r e a s i n g w a t e r l o s s e s d u r i n g low w a t e r p o t e n t i a l s i t u a t i o n s , i t i s n o t s u r p r i s i n g t h a t c o n d i t i o n s p r o m o t i n g l o w w a t e r p o t e n t i a l s i n p l a n t s a l s o i n c r e a s e wax p r o d u c t i o n . F o r e x a m p l e , h i g h r a d i a n t e n e r g y f l u x ( W h i t e c r o s s and A r m s t r o n g 1972, B a k e r 1 9 7 4 ) , l o w h u m i d i t y ( W h i t e c r o s s and A r m s t r o n g 1972, Baker 1974, Hunt and Baker 1982), low s o i l m o i s t u r e (Bengston e t a l . 1978, B a k e r and P r o c o p i o u 1980, S a n e o k a and O g a t a 1 9 8 7 ) , h i g h s a l i n i t y ( D j e b r o u n i 1 9 8 9 ) , and summer months ( F r e e m a n e t a l . 1979, Mayeux e t a l . 1981) have a l l been shown t o be a s s o c i a t e d w i t h i n c r e a s e d wax p r o d u c t i o n . In a d d i t i o n , h i g h t e m p e r a t u r e s cause waxes t o form o v e r t h e p l a n t c u t i c l e ( d e n d r i t e s ) i n s t e a d o f p r o j e c t i n g f r o m i t ( t u b e s ) ( B a k e r 1974). The c r i t i c a l e n v i r o n m e n t a l f a c t o r , however, appears t o be s o i l m o i s t u r e . I f s o i l m o i s t u r e i s low t h e n wax p r o d u c t i o n i s i n c r e a s e d r e g a r d l e s s o f t h e p r e v a i l i n g ambient c o n d i t i o n s (Hunt and Baker 1982). O t h e r e n v i r o n m e n t a l f a c t o r s i n f l u e n c i n g wax p r o d u c t i o n i n c l u d e w i n d , r a i n , a i r p o l l u t i o n , and f e r t i l i z e r l e v e l s . Wind p h y s i c a l l y removes t h e e p i c u t i c u l a r wax from t h e l e a f s u r f a c e s by a b r a s i o n ( H a l l and J o n e s 1961) and r a i n by t h e f o r c e o f i t s i m p a c t ( B a k e r and Hunt 1 9 8 6 ) . A i r p o l l u t i o n , s u c h as S 0 2 > c a n e r o d e t h e e p i c u t i c u l a r wax l a y e r . A t o t h e r t i m e s i t c a u s e s i n c r e a s e s i n wax p r o d u c t i o n ( K o z i o l and C o w l i n g 1981). F e r t i l i z e r s i n c r e a s e p l a n t m e t a b o l i s m (and growth) w h i c h a p p e a r s t o s t i m u l a t e an i n c r e a s e i n t h e amount o f wax produced (Wang e t a l . 1988). -20-The Influence of Ontogenetic Variations on Epicuticular Wax. Wax c o n s t i t u e n t s o f some p l a n t s change w i t h p l a n t age ( B a k e r and Hunt 1981, A v a t o e t a l . 1987, B l a k e r and G r e y s o n 1988) a n d , h e n c e , so may wax morphology. These changes o c c u r because t h e waxes i n t h e s e p l a n t s a r e s y n t h e s i s e d by more t h a n one e l o n g a t i o n - d e c a r b o x y l a t i o n (ED) s y s t e m . F o r e x a m p l e , c o r n has two ED sy s t e m s ( A v a t o e t a l . 1987). The f i r s t s y s tem (ED-I) i s a c t i v e d u r i n g t h e s e e d l i n g s t a g e and y i e l d s a l c o h o l s , a l d e h y d e s , a n d a l k a n e s . The s e c o n d s y s t e m ( E D - I ) i s e f f e c t i v e t h r o u g h o u t t h e p l a n t s l i f e and y i e l d s m a i n l y e s t e r s . The amount o f wax c o v e r i n g t h e l e a f s u r f a c e s o f d i f f e r e n t p l a n t s p e c i e s may a l s o v a r y w i t h l e a f age d e p e n d i n g on t h e r a t e o f wax p r o d u c t i o n v e r s e s t h e r a t e o f l e a f e x p a n s i o n ( B a k e r and Hunt 1981). Wax p r o d u c t i o n (/zg cm - 2) can (1) remain unchanged o r i n c r e a s e w i t h l e a f age, (2 ) d e c r e a s e s t e a d i l y w i t h l e a f age, o r (3) i n c r e a s e f o r a l i m i t e d p e r i o d and the n d e c l i n e so wax c o v e r a g e on ma t u r e l e a v e s i s s l i g h t l y l e s s t h a n on immature l e a v e s ( B a k e r and Hunt 1981). Evidence Support!ng the Theory that Crop Tolerance to Ammonium  Nitrate is Based on Epicuticular Wax. C o n d i t i o n s t h a t i n c r e a s e ( o r d e c r e a s e ) wax p r o d u c t i o n a l s o a p p e a r t o i n c r e a s e ( o r d e c r e a s e ) c r o p t o l e r a n c e t o ammonium n i t r a t e . For example, c r o p t o l e r a n c e i n c r e a s e s i f t h e ammonium n i t r a t e i s a p p l i e d i n t h e a f t e r n o o n o f a warm, d r y sunny day, e s p e c i a l l y i f t h e f i e l d i s f i r s t a l l o w e d t o d r y down ( A g a m a l i a n 1984, N a e g e r l y 1985, Sheer 1985, Agamal i a n 1988). Such c o n d i t i o n s a l s o p r o m o t e e p i c u t i c u l a r wax p r o d u c t i o n . On t h e o t h e r h a n d , when t h e -21-ammonium n i t r a t e i s a p p l i e d a f t e r a good r a i n o r on a f o g g y d a y , t h e c r o p i s o f t e n damaged ( R i g g e r t 1984 and S h e e r 1 9 8 5 ) . U n d e r s u c h c o n d i t i o n s t h e wax l a y e r would n o t be v e r y p r o m i n e n t . In a d d i t i o n , w i n t e r - g r o w n c r o p s a r e more s u s c e p t i b l e t o ammonium n i t r a t e i n j u r y t h a n summer-grown c r o p s ( N a e g e r l y 1985, A g a m a l i a n 1988). I n j u r i e s t o w i n t e r - g r o w n b r o c c o l i i n c l u d e d b l e a c h i n g o f t h e l e a v e s and s t a n d m o r t a l i t y ( A g a m a l i a n 1 9 8 8 ) . Summer-grown b r o c c o l i showed o n l y b u r n i n g on t h e l e a f m a r g i n s and t h e c r o p s t a n d was u n a f f e c t e d ( A g a m a l i a n 1 9 8 8 ) . A s m e n t i o n e d p r e v i o u s l y wax p r o d u c t i o n i s g r e a t e r on summer-grown p l a n t s . P e s t i c i d e a p p l i c a t i o n s b e f o r e t h e ammonium n i t r a t e a p p l i c a t i o n a l s o r e d u c e d c r o p t o l e r a n c e t o t h e s a l t s p r a y ( A g a m a l i a n 1984, N a e g e r l y 1985, Sheer 1985, A g a m a l i a n 1988). A g a m a l i a n (1988) n o t e d a 64 and 48 p e r c e n t l o s s i n b r o c c o l i d r y w e i g h t when t h e ammonium n i t r a t e was a p p l i e d 24 and 48 hours a f t e r a p p l i c a t i o n o f a w e t t i n g a g e n t . A t 72 hours t h e r e was o n l y a 9 p e r c e n t l o s s i n p l a n t d r y w e i g h t . A g a m a l i a n (1988) c o n c l u d e d t h a t a p p l i c a t i o n s o f ammonium n i t r a t e must n o t o c c u r u n t i l 72 h o u r s a f t e r a p e s t i c i d e a p p l i c a t i o n . In a d i f f e r e n t s t u d y , a s u r f a c t a n t used i n t h e a p p l i c a t i o n o f p e s t i c i d e s ( T r i t o n X-100) was shown t o s o l u b i l i z e and c o m p l e t e l y d e s t r o y t h e f i n e wax s t r u c t u r e o f Brassica oleracea v a r . gongylodes ( W o l t e r e t a l . 1988). Ammonium Nitrate Application. P l a n t s o f c o l e c r o p s must be a t t h e t w o - t o - f o u r t r u e l e a f s t a g e b e f o r e t h e ammonium n i t r a t e i s a p p l i e d ( R i g g e r t 1984, 1986 and A g a m a l i a n 1984, 1 9 8 8 ) . R a t e s o f ammonium n i t r a t e a p p l i e d v a r y c o n s i d e r a b l y , and a r e d i c t a t e d by t h e amount o f -22-weed g r o w t h ( R i g g e r t 1 9 8 4 ) . The h i g h e r t h e weed d e n s i t y a n d / o r t h e o l d e r t h e weeds ( i . e . t h e more f o l i a g e p r e s e n t ) , t h e g r e a t e r w i l l be t h e r e q u i r e d volume o f ammonium n i t r a t e . However, a c o n t i n u o u s f i l m s h o u l d n o t be p r e s e n t on t h e l e a f s u r f a c e because t h e l i q u i d may t h e n d r a i n o f f ( M a r t i n and J u n i p e r 1970). T h e r e f o r e , t h e p o i n t j u s t b e f o r e r u n o f f i s t h e most d e s i r a b l e f o r optimum weed c o n t r o l . Low p r e s s u r e (69 t o 138 kPa) a p p l i c a t i o n o f ammonium n i t r a t e i s recommended t o h e l p p r e v e n t f i n e d r o p l e t s o f t h e c h e m i c a l from d r i f t i n g t o t h e g r o w i n g p o i n t o f t h e c r o p ( S h e e r 1985, A g a m a l i a n 1 9 8 8 ) . I n a d d i t i o n , i f t h e f e r t i l i z e r does n o t bead up and r o l l o f f t h e c r o p f o l i a g e , s p r a y i n g s h o u l d be s t o p p e d ( A g a m a l i a n 1984). Weed Species Control Ted. Ammonium n i t r a t e c o n t r o l s many b r o a d l e a f weed s p e c i e s . I n C a l i f o r n i a and O r e g o n , s p e c i e s i d e n t i f i e d a s s u s c e p t i b l e t o ammonium n i t r a t e b u r n i n g i n c l u d e s m a l l f l o w e r e d m a l l o w ( c h e e s e w e e d o r l i t t l e m a l l o w ; Malva parviflora), c h i c k w e e d (Stellaria media), common g r o u n d s e l (Senecio vulgaris), London r o c k e t 1 , b l a c k m u s t a r d (Brassica nigra), b u r n i n g n e t t l e (Urtica dioica), h a i r y n i g h t s h a d e {Solanum sarachoides), r e d r o o t p i g w e e d {Amaranthus retroflexus), p i n e a p p l e w e e d {Matricaria maticarioides), s h e p h e r d ' s - p u r s e (Capsella bursa-pastoris), w i l d r a d i s h (Raphanus raphanist rum), and dog f e n n e l 1 ( A g a m a l i a n 1984, R i g g e r t 1984, A g a m a l i a n 1 9 8 8 ) . Some o f t h e s e weed s p e c i e s a r e i m p o r t a n t weed p r o b l e m s i n C a l i f o r n i a c o l e c r o p s . These i n c l u d e s m a l l f l o w e r e d m a l l o w , Scientific name was not a v a i l a b l e . -23-s h e p h e r d ' s - p u r s e , h a i r y n i g h t s h a d e , common g r o u n d s e l , and p i n e a p p l e weed (A g a m a l i a n 1984, 1988). O t h e r weeds a r e t o l e r a n t t o ammonium n i t r a t e b u r n i n g . I n C a l i f o r n i a a n d O r e g o n , r e s i s t a n t w e e d s i d e n t i f i e d i n c l u d e l a m b ' s - q u a r t e r s {Chenopodium album), n e t t l e l e a f g o o s e f o o t (C. murale), a n n u a l s o w t h i s t l e (Sonchus oleraceus), p u r s l a n e (Portulaca oleracea), annual b l u e g r a s s {Poa annua) and b a r n y a r d g r a s s (Echinocloa crusgalii) ( A g a m a l i a n 1984, R i g g e r t 1984, A g a m a l i a n 1 9 8 8 ) . F o r t u n a t e l y , t h e s e weeds a r e c o n t r o l l e d by a pre-emergent t r e a t m e n t o f t r i f l u r a l i n o r DCPA. The e n v i r o n m e n t can a l t e r weed s u s c e p t i b i l i t y t o ammonium n i t r a t e . C o o l , wet c o n d i t i o n s r e s u l t i n l e s s weed c o n t r o l ( R i g g e r t 1986). Weed age a l s o a l t e r s weed s u s c e p t i b i l i t y . The o l d e r t h e p l a n t s t h e p o o r e r t h e c o n t r o l . F o r example, weed c o n t r o l a t t h e o n e - t o - f o u r t r u e l e a f s t a g e o f t h e s u s c e p t i b l e s p e c i e s mentioned above ( e x c e p t dog f e n n e l and b l a c k mustard) ranged from 92 t o 99 p e r c e n t ( A g a m a l i a n 1 9 8 8 ) . A t t h e f i v e - t o - s e v e n t r u e l e a f s t a g e c o n t r o l d e c r e a s e d t o 41 t o 77 p e r c e n t ( A g a m a l i a n 1988). A g a m a l i a n (1988) n o t e d t h a t weed b u r n i n g s t i l l o c c u r s when t h e s u s c e p t i b l e s p e c i e s a r e o l d e r (5 t o 7 t r u e l e a f s t a g e ) , but t h e weeds regrow. R e g a r d l e s s o f p l a n t age, r e s i s t a n t weed s p e c i e s do n o t v a r y i n t h e i r t o l e r a n c e t o ammonium n i t r a t e (0 p e r c e n t c o n t r o l ) , e x c e p t f o r a n n u a l s o w t h i s t l e ( A g a m a l i a n 1 9 8 8 ) . I n i t i a l ( o n e - t o - f o u r t r u e l e a f s t a g e ) c o n t r o l o f annual s o w t h i s t l e was 32 p e r c e n t , but t h i s d e c r e a s e d t o 0 p e r c e n t when t h e p l a n t s were o l d e r ( f i v e - t o - s e v e n t r u e l e a f s t a g e ) ( A g a m a l i a n 1988). A d i f f e r e n t n i t r o g e n f e r t i l i z e r , ammonium t h i o s u l f a t e ( 1 2 - 0 - 0 - 2 4 ) , -24-gave 54, 88, and 93 p e r c e n t .control o f Jim H i l l m u s t a r d 2 a t r a t e s o f 93, 186, and 280 L h a " 1 r e s p e c t i v e l y (Cudney and O r l o f f 1 9 8 8 ) . R u s s i a n t h i s t l e (Salsola pestifer) was more t o l e r a n t . I t was o n l y c o n t r o l l e d 18, 28, and 38 p e r c e n t r e s p e c t i v e l y . Varietal Differences in Crop Tolerance. A d i r e c t e d s p r a y o f ammonium n i t r a t e (750 L h a - 1 ; 20 p e r c e n t N) a f f e c t s v a r i o u s b r o c c o l i c u l t i v a r s d i f f e r e n t l y ( A g a m a l i a n 1988). F o r example, a d i r e c t e d s p r a y r e d u c e d t h e s t a n d o f F u t u r a by 8 p e r c e n t , b u t d i d n o t s i g n i f i c a n t l y e f f e c t Emperor, E x c a l i b u r , Green Duke, Green V a l i a n t , Premium Cr o p , and Shogun s t a n d s . The d i r e c t e d s p r a y d e c r e a s e d growth (measured a t 14 days a f t e r ammonium n i t r a t e a p p l i c a t i o n ) o f E x c a l i b u r , F u t u r a , Premium Crop, and Shogun w h i l e Emperor, Green Duke, and Green V a l i a n t growth was not a f f e c t e d . However, c r o p y i e l d s o f a l l t h e c u l t i v a r s e x c e p t F u t u r a were not s i g n i f i c a n t l y d i f f e r e n t from t h e c o n t r o l . The e f f e c t o f a t o p i c a l ( o v e r t h e e n t i r e p l a n t ) a p p l i c a t i o n o f ammonium n i t r a t e was a l s o s t u d i e d ( A g a m a l i a n 1988). S t a n d m o r t a l i t y i n F u t u r a i n c r e a s e d t o 10 p e r c e n t . Growth a t 14 days was s i g n i f i c a n t l y r e d u c e d i n Emperor, E x c a l i b u r , F u t u r a , Green V a l i a n t , Premium C r o p , a n d Shogun w h i l e o n l y Green Duke was not a f f e c t e d . The d e c r e a s e d growth o f t h e c u l t i v a r s ( e x c e p t Green Duke) t r a n s l a t e d i n t o r e d u c e d y i e l d s . In c o n t r a s t t o Ag a m a l i a n ' s f i n d i n g , R i g g e r t (1986) f o u n d b r o c c o l i y i e l d i n c r e a s e d w i t h t h e ammonium n i t r a t e a p p l i c a t i o n . R i g g e r t (1986) Scient i f ic name was not a v a i l a b l e . -25-s p e c u l a t e d t h a t t h i s was due t o t h e h i g h e r r a t e o f ammonium n i t r a t e a p p l i e d and t h e e a r l y d a t e o f i t s a p p l i c a t i o n . R i g g e r t (1986) s u g g e s t e d t h a t t h e t i m e o f a p p l i c a t i o n c o i n c i d e d w i t h c r o p demand f o r n i t r o g e n . C a u l i f l o w e r r e s p o n d s d i f f e r e n t l y t o ammonium n i t r a t e t h a n does b r o c c o l i . I t s u f f e r s more f o l i a r damage and i n some i n s t a n c e s t h e g r o w i n g p o i n t i s d e s t r o y e d , r e s u l t i n g i n d i s t o r t e d c u r d d e v e l o p m e n t ( R i g g e r t 1986, A g a m a l i a n 1988). F o r e x a m p l e , R i g g e r t (1986) r e p o r t e d t h a t t r e a t m e n t s w h i c h d i d n o t a f f e c t b r o c c o l i g r o w t h a n d y i e l d , d e c r e a s e d c a u l i f l o w e r y i e l d . -26-3. L a m b ' s - q u a r t e r s I n t e r f e r e n c e w i t h D i r e c t Seeded B r o c c o l i 3.1 I n t r o d u c t i o n B r o c c o l i (Brassica oleracea v a r . botrytis) i s a h i g h v a l u e c r o p whose g r o s s v a l u e i n B r i t i s h C o l u m b i a (B.C.) was $5,220 ha" 1 i n 1985 and $4',455 ha" 1 i n 1986 (BCMAF 1985, 1 9 8 6 ) . Weeds have been e s t i m a t e d t o c a u s e a 20 p e r c e n t a v e r a g e annual r e d u c t i o n i n b r o c c o l i y i e l d s i n t h e P a c i f i c r e g i o n o f t h e U n i t e d S t a t e s ( C h a n d l e r e t a l . 1984). D e s p i t e t h e l a r g e y i e l d l o s s e s and h i g h v a l u e o f t h e c r o p , l i t t l e work has been done on weed c o m p e t i t i o n i n b r o c c o l i ( A g a m a l i a n 1976, 1983). L a m b ' s - q u a r t e r s (Chenopodium album L . ) , w h i c h i s r a n k e d as one o f t h e w o r s t weeds o f c u l t i v a t e d c r o p s (Holm e t a l . 1977), i s a s e r i o u s p r o b l e m i n t h e Lower F r a s e r V a l l e y o f B.C.. The o b j e c t i v e o f t h i s s t u d y was t o d e t e r m i n e t h e e f f e c t o f l a m b ' s - q u a r t e r s i n t e r f e r e n c e on t h e growth and y i e l d o f d i r e c t seeded b r o c c o l i . 3.2 M a t e r i a l s and Methods F i e l d e x p e r i m e n t s were c o n d u c t e d a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a P l a n t S c i e n c e F i e l d L a b o r a t o r y i n 1987 and 1988. S o i l ( B o s e , sandy loam w i t h 6.6% o r g a n i c m a t t e r ) samples were t e s t e d each s p r i n g t o d e t e r m i n e n u t r i e n t s t a t u s and pH. The f i e l d r e c e i v e d 69, 188, and 130 kg ha" 1 N, P, and K r e s p e c t i v e l y i n 1987, and 54, 96, and 66 kg ha" 1 N, P, and K r e s p e c t i v e l y i n 1988. S o i l pH was 6.2 i n 1987. In 1988 t h e pH was 5.3, and t h e r e f o r e , 5.2 t ha" 1 o f a f i n e mesh d o l o m i t e l i m e (amount d e t e r m i n e d by S M P - b u f f e r method; Shoemaker e t a l . 1961) was a p p l i e d . N a t u r a l weed p o p u l a t i o n s were c o n t r o l l e d w i t h a p r e p l a n t - t r e a t m e n t o f t h e s o i l f u m i g a n t dazomet ( B a s a m i d ) , w h i c h was a p p l i e d a t a r a t e o f -27-3.81 kg 100 n f 2 i n 1987 and 3.25 kg 100 n f 2 i n 1988. The f u m i g a n t was d i s k e d i n t o t h e s o i l and t h e s u r f a c e was s e a l e d u s i n g a p a c k e r . A f t e r 2 t o 3 weeks t h e s o i l was r o t o t i l l e d t o r e l e a s e t h e s t e r i l a n t fumes. A r a n d o m i z e d c o m p l e t e b l o c k d e s i g n w i t h f o u r r e p l i c a t e s and s i x l a m b ' s - q u a r t e r s d e n s i t i e s ( 0 , 3, 8, 10, 12, 15 p l a n t s n f 2 ) was used. In 1988, t h e 8 p l a n t s n f 2 t r e a t m e n t had o n l y 3 r e p l i c a t e s . G e r m i n a t i o n t e s t s were used t o e s t i m a t e t h e amount o f l a m b ' s - q u a r t e r s seed r e q u i r e d t o a c h i e v e t h e above d e n s i t i e s . I m m e d i a t e l y a f t e r t h e b r o c c o l i had been d i r e c t seeded i n a row down t h e m i d d l e o f a p l o t , t h e l a m b ' s - q u a r t e r s s e e d was m i x e d w i t h s a n d and b r o a d c a s t o v e r t h e t o t a l p l o t a r e a (1 m x 5 m). The weed seeds were l i g h t l y r a k e d i n t o t h e s o i l w h i c h was t h e n packed u s i n g a r o l l e r . The p l a n t i n g d a t e s were 23 Jun e , 1987 and 4 J u l y , 1988. The i n s e c t i c i d e d i a z i n o n ( B a s u d i n ) ( t o c o n t r o l r o o t m a ggots), and t h e f u n g i c i d e s c a p t a n ( C a p t a n , O r t h o c i d e ) and c h l o r o t h a l o n i l ( B r a v o ) ( t o c o n t r o l d a m p i n g o f f ) w e r e a p p l i e d as n e c e s s a r y . L a m b ' s - q u a r t e r s s e e d l i n g s were t h i n n e d t o t h e d e s i r e d d e n s i t i e s and s e e d l i n g s o f o t h e r weeds were removed by hand. B r o c c o l i p l a n t s were t h i n n e d and h a r v e s t e d f o r s h o o t d r y w e i g h t d a t a as t h e season p r o g r e s s e d . The s h o o t d r y w e i g h t s a m p l e s were t a k e n a t w e e k l y i n t e r v a l s s t a r t i n g a t 29 (1988) t o 30 (1987) days a f t e r s e e d i n g and c u l m i n a t e d when t h e f l o w e r buds begun t o f o r m . The f i n a l s p a c i n g o f b r o c c o l i p l a n t s t h a t d e v e l o p e d mature heads was a p p r o x i m a t e l y 30 t o 50 cm. M a t u r e b r o c c o l i h e a d s , c u t t o 20 cm l e n g t h s , were h a r v e s t e d t o d e t e r m i n e t o t a l and m a r k e t a b l e (heads >10 cm a c r o s s ) y i e l d s . The number o f heads h a r v e s t e d p e r p l o t was r e c o r d e d . In b o t h y e a r s t h e t o t a l number o f heads p e r p l o t e q u a l l e d t h e number o f -28-b r o c c o l i p l a n t s p e r p l o t . Average head w e i g h t s and y i e l d ( t ha" 1) were c a l c u l a t e d . U s i n g t h e p r o c e d u r e d e s c r i b e d b y C o u s e n s ( 1 9 8 8 ) , l o g t r a n s f o r m a t i o n s o f s h o o t d r y w e i g h t s were made t o o b t a i n a homogeneous v a r i a n c e p o p u l a t i o n . A S y s t a t s t a t i s t i c a l package ( W i l k i n s o n 1988) was used t o f i t t h e d a t a a t each d e n s i t y t o t h e model: l o g ( y i e l d ) = b ^ T ) + b 2 ( l / T ) (1) where b j and b2 a r e s l o p e c o n s t a n t s and T i s t h e t i m e i n days a f t e r s e e d i n g t h e c r o p ( F i g . IB and I D ) . B r o c c o l i y i e l d s were f i t t e d t o t h e r e c t a n g u l a r h y p e r b o l a : y = y w f (1 - 1D/(1 + ID/a)) (2) where y = y i e l d , y = weed f r e e y i e l d , i = p e r c e n t y i e l d l o s s when t h e weed d e n s i t y i s low, a = a s y m p t o t i c p e r c e n t y i e l d l o s s , and D = weed d e n s i t y (Cousens 1985, 1988). G o o d n e s s o f f i t was c a l c u l a t e d u s i n g t h e f o r m u l a : R 2 = 1 -( r e s i d u a l S . S . ) / ( t o t a l S .S.), where S.S. = sum o f s q u a r e s . The n o n l i n e a r t o t a l S.S. was c a l c u l a t e d a s : r e g r e s s i o n S.S. + r e s i d u a l S.S. - ( n y 2 ) , w h e r e n = number o f c a s e s and y = mean o f t h e d e p e n d e n t v a r i a b l e ( P e r s o n a l c o m m u n i c a t i o n , Dr. P a t r i c k J . F l e u r y , SYSTAT, I n c . ) . 3.3 R e s u l t s and D i s c u s s i o n G e n e r a l l y , t h e n e g a t i v e e f f e c t o f weed i n t e r f e r e n c e on b r o c c o l i g rowth i n c r e a s e d w i t h i n c r e a s i n g weed d e n s i t y and t i m e a f t e r s e e d i n g , e x c e p t f o r 3 p l a n t s m"2 i n 1988 ( F i g . 1 ) . I n t e r f e r e n c e by 15 l a m b ' s - q u a r t e r s p l a n t s m"2 r e d u c e d t h e biomass o f b r o c c o l i p l a n t s by 71 t o 73 p e r c e n t compared t o t h e weed f r e e c o n t r o l a t 57 t o 58 days a f t e r -29-F i g . 1. T i m e - c o u r s e o f t h e e f f e c t o f l a m b ' s - q u a r t e r s d e n s i t i e s on b r o c c o l i s h o o t d r y w e i g h t i n ( A ) 1987 and ( C ) 1 9 8 8 . L a m b ' s - q u a r t e r s d e n s i t i e s ( p l a n t s m"2) a r e i n d i c a t e d on t h e f i g u r e . Data was f i t t e d t o t h e model l o g ( y i e l d ) = b ^ T ) + b 2 ( l / T ) ( E q u a t i o n 1 d e s c r i b e d on p . 2 8 ) . I n 1987 ( B ) r e g r e s s i o n e q u a t i o n s w e r e : 0 . 0 4 2 ( T ) - 2 5 . 2 ( 1 / T ) ( R 2 = 0 . 9 7 ) ; 0.037(T)-20.2(1/T) (R 2=0.95); 0 . 0 3 3 ( T ) - 1 4 . 3 ( 1 / T ) ( R 2 = 0 . 9 1 ) ; 0 . 0 3 2 ( T ) - 1 3 . 7 ( 1 / T ) (R 2=0.89); 0.032(T)-13.1(1/T) (R 2=0.92); and 0.029(T)-11.7(1/T) (R 2=0.88) f o r 0, 3, 8, 10, 12, and 15 p l a n t s n f 2 , r e s p e c t i v e l y . In 1988 (D) r e g r e s s i o n e q u a t i o n s w e r e : 0 . 0 4 3 ( T ) - 2 5 . 1 ( 1 / T ) ( R 2 = 0 . 9 5 ) ; 0 . 0 3 5 ( T ) - 1 8 . 2 ( 1 / T ) ( R 2 = 0 . 9 0 ) ; 0 . 0 3 7 ( T ) - 1 9 . 5 ( 1 / T ) (R 2=0.96); 0.037(T)-19.3(1/T) (R 2=0.93); 0 . 0 3 3 ( T ) - l 2 . 3 ( l / T ) (R 2=0.86); 0 . 0 3 1 ( T ) - 1 5 . 7 ( 1 / T ) ( R 2 = 0 . 8 5 ) f o r 0, 3, 8, 1 0 , 1 2 , a n d 15 p l a n t s m"2, r e s p e c t i v e l y . A l l e q u a t i o n s were s t a t i s t i c a l l y s i g n i f i c a n t (p<0.01). -oe--31-s e e d i n g ( F i g 1A and 1 C ) . The t i m e when l a m b ' s - q u a r t e r s i n t e r f e r e n c e f i r s t a f f e c t e d b r o c c o l i growth i s shown by t h e i n t e r c e p t s o f t h e c u r v e s d e s c r i b i n g b r o c c o l i growth a t each s p e c i f i c weed d e n s i t y w i t h t h e weed f r e e c o n t r o l ( F i g . IB and I D ) . Crop g r o w t h was i n i t i a l l y a f f e c t e d by weed i n t e r f e r e n c e a t 28 t o 36 da y s a f t e r s e e d i n g i n d e p e n d e n t o f weed d e n s i t y . Weed d e n s i t y - c r o p y i e l d r e l a t i o n s h i p c u r v e s showed t h a t t o t a l and m a r k e t a b l e y i e l d s i n t h e absence o f weed i n t e r f e r e n c e were 15.0 t ha" 1 and 13.4 t ha" 1 r e s p e c t i v e l y i n 1987 and 14.5 t ha" 1 f o r b o t h i n 1988 ( F i g 2 ) . L a m b ' s - q u a r t e r s c o m p e t i t i o n had a p r o f o u n d e f f e c t on b r o c c o l i y i e l d ; one l a m b ' s - q u a r t e r s p l a n t m"2 r e d u c e d t o t a l y i e l d by 18 t o 20 p e r c e n t and m a r k e t a b l e y i e l d by 22 t o 37 p e r c e n t . F i f t e e n p l a n t s m"2 r e d u c e d t o t a l and m a r k e t a b l e y i e l d s by 78 and 96 p e r c e n t r e s p e c t i v e l y i n 1987 and by 50 and 58 p e r c e n t r e s p e c t i v e l y i n 1988. L a m b ' s - q u a r t e r s i n t e r f e r e n c e r e d u c e d t o t a l y i e l d by r e d u c i n g a v e r a g e head w e i g h t and n o t by l o w e r i n g t h e number o f heads p e r p l o t ( F i g . 3; T a b l e 1 ) . One l a m b ' s - q u a r t e r s p l a n t m"2 r e d u c e d t h e a v e r a g e head w e i g h t by 27 p e r c e n t i n b o t h y e a r s ( F i g . 3 ) . F i f t e e n p l a n t s m"2 r e d u c e d t h e ave r a g e head w e i g h t by 79 p e r c e n t i n 1987 and 58 p e r c e n t i n 1988 ( F i g . 3 ) . The ave r a g e m a r k e t a b l e head w e i g h t was a l s o l o w e r i n t h e p r e s e n c e o f l a m b ' s - q u a r t e r s ( d a t a n o t s h o w n ) . In a d d i t i o n , n o t a l l b r o c c o l i p l a n t s g r o w n w i t h t h e weed p r o d u c e d m a r k e t a b l e h e a d s , e s p e c i a l l y i n 1987 when t h e number o f m a r k e t a b l e heads p e r p l o t was d r a s t i c a l l y r e d u c e d by weed i n t e r f e r e n c e ( T a b l e 1 ) . R 2 v a l u e s f o r b r o c c o l i y i e l d and a v e r a g e head w e i g h t were much l o w e r i n 1988 t h a n 1987 ( F i g . 2 and 3 ) . However, t h e v a l u e s c a l c u l a t e d -32-F i g . 2. The e f f e c t o f l a m b ' s - q u a r t e r s d e n s i t i e s on ( O ) t o t a l and (•) m a r k e t a b l e y i e l d f o r (A) 1987 and (B) 1988. Data were f i t t e d w i t h a r e c t a n g u l a r h y p e r b o l i c model ( E q u a t i o n 2 d e s c r i b e d on p . 2 8 ) . In 1987, r e g r e s s i o n c o e f f i c i e n t s were: y =15.0, i = 0 . 2 2 , a=1.01 and y =13.4, i = 0 . 5 6 , a=1.09 f o r WT WT t o t a l a n d m a r k e t a b l e y i e l d , r e s p e c t i v e l y . I n 1 9 8 8 r e g r e s s i o n c o e f f i c i e n t s were: y^ f=14.5, i = 0 . 3 1 , a=0.56 and y ,=14.5, i = 0 . 3 4 , a=0.65 f o r t o t a l and m a r k e t a b l e y i e l d , r e s p e c t i v e l y . In a l l c a s e s t h e model was s t a t i s t i c a l l y s i g n i f i c a n t (p<0.01). L A M B ' S - Q U A R T E R S D E N S I T Y (p lants m" 2) -34-F i g . 3. The e f f e c t o f l a m b ' s - q u a r t e r s d e n s i t y on b r o c c o l i h e a d w e i g h t f o r ( O ) 1987 and (•) 1988. A v e r a g e b r o c c o l i head w e i g h t s were f i t t e d w i t h a r e c t a n g u l a r h y p e r b o l i c model d e s c r i b e d i n t h e t e x t . R e g r e s s i o n c o e f f i c i e n t s w e r e : y =693, i=0.38, a=0.91 and y =618, i=0.49, a=0.63 f o r 1987 wf wf a n d 1 9 8 8 , r e s p e c t i v e l y . I n a l l c a s e s t h e model was s t a t i s t i c a l l y s i g n i f i c a n t (p<0.01). -35-co -H (6) 1M 0V3H -36-T a b l e 1. The number o f t o t a l and m a r k e t a b l e heads p e r p l o t i n 1987 and 1988. Weed T o t a l Heads M a r k e t a b l e Heads D e n s i t y ( p l a n t s ra" ) 1987 1988 1987 1988 0 10 ± 2 11 ± 2 8 ± 2 1 1 + 3 3 12 + 2 12 ± 2 4 ± 3 9 ± 3 8 11 ± 2 14 ± 3 1 ± 2 8 ± 4 10 13 ± 2 12 + 5 1 ± 1 11 ± 2 12 12 ± 1 13 ± 3 1 ± 1 8 + 3 15 9 ± 1 13 ± 2 1 ± 1 4 ± 3 A l l v a u l e s a r e means + s t a n d a r d d e v i a t i o n . T o t a l head number a l s o i n d i c a t e s t h e number o f p l a n t s p e r p l o t . -37-f o r 1988 a r e n o t uncommon f o r f i e l d e x p e r i m e n t s where e n v i r o n m e n t a l c o n d i t i o n s f l u c t u a t e and p l a n t pathogens and i n s e c t s can a t t a c k t h e c r o p a n d / o r weed. Such e n v i r o n m e n t a l and p e s t f a c t o r s c a n i n f l u e n c e o r change t h e more d i r e c t weed-crop r e l a t i o n s h i p . T h e r e f o r e , t h e l o w e r R 2 v a l u e s f o r 1988 s u g g e s t t h a t e n v i r o n m e n t a l a n d / o r p e s t f a c t o r s had a s t r o n g e r i n f l u e n c e on w e e d - c r o p i n t e r a c t i o n s i n 1988 t h a n i n 1987. Indeed, downy mildew was no t e d on some l a m b ' s - q u a r t e r s p l a n t s i n 1988, b u t n o t i n 1987. However, downy m i l d e w may n o t have been t h e o n l y f a c t o r e f f e c t i n g weed-crop i n t e r a c t i o n s . The e n v i r o n m e n t and o t h e r b i o t i c f a c t o r s may a l s o have a l t e r e d t h e weed-crop r e l a t i o n s h i p t h e r e b y c o n t r i b u t i n g t o t h e l o w e r R 2 v a l u e s seen i n 1988. G r e a t e r y i e l d l o s s e s o b s e r v e d i n 1987 m i g h t be t h e r e s u l t o f e a r l i e r p l a n t i n g (by 11 d a y s ) . In s u g a r b e e t , a t e n day d e l a y i n t h e sowing o f l a m b ' s - q u a r t e r s seeds r e s u l t e d i n t h e l a t e seeded weeds b e i n g s h o r t e r , h a v i n g a l o w e r l e a f a r e a i n d e x , and f i n i s h i n g g r o w t h a t t h e same t i m e as t h e e a r l i e r sown weeds ( J o e n j e and K r o p f f 1987). Presumably f l o w e r i n g , i n d u c e d by s h o r t e n i n g day l e n g t h , r e s t r i c t e d t h e v e g e t a t i v e g r o w t h o f t h e weed and r e d u c e d i t s a b i l i t y t o compete w i t h t h e c r o p ( J o e n j e and K r o p f f 1987). The e f f e c t o f l a m b ' s - q u a r t e r s i n t e r f e r e n c e on b r o c c o l i was q u i t e s e v e r e compared t o some o t h e r c r o p s ( M a i l l e t t e 1986; B l a c k s h a w e t a l . 1987; Conn and Thomas 1987). F i f t e e n l a m b ' s - q u a r t e r s p l a n t s n f 2 r e d u c e d t h e t o t a l b r o c c o l i y i e l d by 50 t o 78 p e r c e n t . T h i s i s much g r e a t e r t h a n t h e 20 t o 25 p e r c e n t y i e l d r e d u c t i o n w i t h 20 t o 80 l a m b ' s - q u a r t e r s p l a n t s n f 2 i n s p r i n g r a p e s e e d ( B l a c k s h a w e t a l . 1 9 8 7 ) , t h e 23 t o 36 p e r c e n t r e d u c t i o n w i t h 150 t o 1300 p l a n t s n f 2 i n s p r i n g b a r l e y (Conn and Thomas 1987), and t h e 23 p e r c e n t r e d u c t i o n w i t h 571 p l a n t s n f 2 i n -38-wheat ( M a i l l e t t e 1986). On t h e o t h e r hand, a l a m b ' s - q u a r t e r s d e n s i t y o f 8 p l a n t s n f 2 r e d u c e d s u g a r b e e t y i e l d by 48 p e r c e n t ( S c h w e i z e r 1 9 8 3 ) , w h i c h i s c o m p a r a b l e t o t h e r e d u c t i o n o b s e r v e d i n t h i s s t u d y ( F i g . 2 ) . The d r a s t i c r e d u c t i o n o f b r o c c o l i y i e l d by l a m b ' s - q u a r t e r s i n t h i s s t u d y can be l i n k e d t o t h e weed g r o w i n g t a l l e r t h a n t h e c r o p ( F i g . 4 ) . L a m b ' s - q u a r t e r s p l a n t s can r e a c h h e i g h t s o f 1.3 t o 1.6 m ( J o e n j e and K r o p f f 1987, S c h w e i z e r 1983), w h i l e b r o c c o l i p l a n t s o n l y grow t o about 0.60 m. In c o m p e t i t i o n e x p e r i m e n t s w i t h s u g a r b e e t , l a m b ' s - q u a r t e r s p l a n t s grew a p p r o x i m a t e l y 2.4 t i m e s t a l l e r t h a n t h e c r o p ( J o e n j e and K r o p f f 1987). As a r e s u l t t h e c r o p s u f f e r e d s e v e r e r e d u c t i o n s i n y i e l d ; 43 p e r c e n t a t 5.5 l a m b ' s - q u a r t e r s n f 2 ( J o e n j e and K r o p f f 1987) and 13 t o 48 p e r c e n t a t 2 t o 8 l a m b ' s - q u a r t e r s m"2 r e s p e c t i v e l y ( S c h w e i z e r 1983). J o e n j e and K r o p f f ( 1 9 8 7 ) s u g g e s t e d t h a t r e l a t i v e h e i g h t i s more i m p o r t a n t t h a n r e l a t i v e l e a f a r e a i n t h e c o m p e t i t i o n f o r l i g h t . H e i g h t d i f f e r e n c e s b e t w e en a c r o p and weed s p e c i e s d e p e n d on r e l a t i v e t i m e s o f emergence and r e l a t i v e growth r a t e s . B l a c k s h a w e t a l . ( 1 9 8 7 ) r e l a t e d t h e p o o r c o m p e t i t i v e a b i l i t y o f l a m b ' s - q u a r t e r s i n r a p e s e e d t o i t s l a t e e m e rgence (7 t o 10 d a y s a f t e r t h e r a p e s e e d ) . M a i l l e t t e (1986) o b s e r v e d t h a t wheat grew f a s t e r and d o m i n a t e d t h e l a m b ' s - q u a r t e r s p l a n t s f r o m t h e b e g i n n i n g . T h e r e f o r e , t h e wheat was a b l e t o m a i n t a i n i t s l e a v e s above t h e weed a t l e a s t u n t i l i t r e a c h e d i t s r e p r o d u c t i v e p h a s e . In c o n t r o l l e d e n v i r o n m e n t s t u d i e s , E l b e r s e and K r u y f (1979) found t h a t s p r i n g b a r l e y began i t s e x p o n e n t i a l growth a t an e a r l i e r s t a g e t h a n l a m b ' s - q u a r t e r s and t h i s a l l o w e d i t t o occupy most o f t h e a r e a b e f o r e t h e l a m b ' s - q u a r t e r s . -39-L a m b ' s - q u a r t e r s and b r o c c o l i a t (a) 31 days and (b) 43 days a f t e r s e e d i n g (1988) showing d i f f e r e n c e s i n g r o w t h . - 40 --41-In t h e c a s e o f b r o c c o l i and l a m b ' s - q u a r t e r s , b o t h have s i m i l a r emergence t i m e and g r o w t h . F o r i n s t a n c e , b r o c c o l i r e q u i r e s a p p r o x i m a t e l y 11 days (mean s o i l t e m p e r a t u r e = 13.4°C) t o a c h i e v e 50 p e r c e n t emergence ( H e g a r t y 1 9 7 4 ) , w h i c h i s c o m p a r a b l e t o t h e 10 t o 14 days r e q u i r e d by l a m b ' s - q u a r t e r s (mean s o i l t e m p e r a t u r e = 13.3°C) (Weaver e t a l . 1 9 8 8 ) . D e p e n d i n g on t h e amount o f n i t r o g e n and w a t e r a v a i l a b l e , b r o c c o l i r e q u i r e s 58 t o 76 days t o a t t a i n half-maximum d r y m a t t e r a c c u m u l a t i o n ( B e v e r l y e t a l . 1986) w h i l e l a m b ' s - q u a r t e r s r e q u i r e s 75-85 days ( J o e n j e and K r o p f f 1987). However, when one c o n s i d e r s t h a t l a m b ' s - q u a r t e r s can g r o w 2 o r 3 t i m e s t a l l e r t h a n b r o c c o l i , t h e n t h e s i m i l a r i t i e s i n emergence and growth p a t t e r n s w i l l r e s u l t i n t h e weed b e i n g t a l l e r t h a n t h e c r o p . T h e r e f o r e , t h e weed w i l l i n t e r c e p t more l i g h t and r e d u c e t h e growth r a t e and y i e l d o f t h e c r o p . -42-4. Weed control in Cole Crops and Onion Using an Ammonium Nitrate Solution 4.1 Introduction The c u r r e n t l y r e g i s t e r e d h e r b i c i d e s ( t r i f l u r a l i n , DCPA) f o r c o l e c r o p s i n B r i t i s h C o l u m b i a (B.C.) g i v e poor weed c o n t r o l i n s o i l s w i t h h i g h o r g a n i c m a t t e r and do n o t c o n t r o l g r o u n d s e l , smartweeds and weeds o f t h e m u s t a r d f a m i l y . T h e r e f o r e , f i e l d s t h a t have grown c o l e c r o p s f o r a n u m b e r o f y e a r s h a v e t h e f o l l o w i n g weeds as a m a j o r p r o b l e m : s h e p h e r d ' s - p u r s e , w i l d m u s t a r d , l a d y ' s - t h u m b , s m a r t w e e d , and common g r o u n d s e l ( p e r s o n a l c o m m u n i c a t i o n Mr. M a r k Sweeney, B.C.A.M.F.). G r o w e r s i n C a l i f o r n i a and O r e g o n h a v e a c h i e v e d some s u c c e s s i n c o n t r o l l i n g b r o a d l e a f weeds i n c o l e c r o p s and o n i o n s by a post-emergence a p p l i c a t i o n o f an ammonium n i t r a t e s o l u t i o n ( 2 0 - 0 - 0 ) . T h i s t r e a t m e n t k i l l s weeds by b u r n i n g w i t h i n a few hours o f a p p l i c a t i o n . S e l e c t i v i t y o f t h i s m e t h o d i s b e l i e v e d t o d e p e n d on t h e t h i c k n e s s o f l e a f e p i c u t i c u l a r wax, w h i c h i s s i g n i f i c a n t l y i n f l u e n c e d by e n v i r o n m e n t a l c o n d i t i o n s . Because t h e c l i m a t e and weed p o p u l a t i o n o f B.C. d i f f e r f rom t h o s e i n C a l i f o r n i a and Oregon, i t was not known i f t h i s method would be f e a s i b l e under ou r l o c a l c o n d i t i o n s . T h e r e f o r e , t h e o b j e c t i v e o f t h i s s t u d y was t o d e t e r m i n e (1) t h e r e l a t i v e s u s c e p t i b i l i t y o f d i f f e r e n t weed s p e c i e s t o ammonium n i t r a t e , (2) t h e e f f e c t o f weed d e n s i t y on weed c o n t r o l by ammonium n i t r a t e , and (3) t h e r e l a t i v e s u s c e p t i b i l i t y o f v a r i o u s b r o c c o l i , c a u l i f l o w e r , c a b b a g e , B r u s s e l s s p r o u t s , and o n i o n c u l t i v a r s t o ammonium n i t r a t e . -43-4.2 Relative Susceptibility of Different Weed Species and the Effect o f Shepherd's-purse Density on Weed Control (i) Materials and Methods F i e l d e x p e r i m e n t s were c o n d u c t e d a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a P l a n t S c i e n c e F i e l d L a b o r a t o r y i n 1987, 1988, and 1989. S o i l ( B o se, sandy loam w i t h 6.6 p e r c e n t o r g a n i c m a t t e r ) samples were t e s t e d each s p r i n g t o d e t e r m i n e n u t r i e n t s t a t u s and pH. Lime r e q u i r e m e n t s were d e t e r m i n e d u s i n g t h e S M P - b u f f e r method (Shoemaker e t a l . 1961). The i n s e c t i c i d e d i a z i n o n ( B a s u d i n ) ( t o c o n t r o l r o o t m a g g o t s ) and t h e f u n g i c i d e s c a p t a n ( C a p t a n , O r t h o c i d e ) and c h l o r o t h a l o n i l ( B r a v o ) ( t o c o n t r o l damping o f f ) were a p p l i e d as n e c e s s a r y . A s o l u t i o n o f ammonium n i t r a t e i n w a t e r (Ammonium N i t r a t e 20) was p u r c h a s e d f r o m A g r i . Chem. I n c . ( W a s h i n g t o n , U.S.A.). I t c o n t a i n e d 57.1 p e r c e n t ammonium n i t r a t e (20 p e r c e n t N). C o n c e n t r a t i o n s l o w e r t h e n 57.1 p e r c e n t ammonium n i t r a t e were o b t a i n e d by d i l u t i n g t h e o r i g i n a l s o l u t i o n w i t h w a t e r . Ammonium n i t r a t e c o n c e n t r a t i o n s ( 5 7 . 1 , 42.8, 28.6, 21.4 and 0 p e r c e n t ) a r e e x p r e s s e d t h r o u g h o u t as p e r c e n t N ( 2 0 , 15, 10, 7.5 and 0 p e r c e n t ) . Relative Susceptibility of Meed Species. The f i e l d r e c e i v e d 89, 137, and 198 kg h a - 1 N, P, K r e s p e c t i v e l y i n 1987. S o i l pH was 6.2 so no l i m e was a d d e d . A r a n d o m i z e d c o m p l e t e b l o c k d e s i g n w i t h f o u r r e p l i c a t e s p e r t r e a t m e n t was u s e d . B r o c c o l i ( c v . Emperor) and o n i o n ( c v . W hite L i s b o n ) were d i r e c t seeded on 4 June 1987 i n a row down t h e m i d d l e o f 1 m x 5 m p l o t s . The n a t u r a l weed p o p u l a t i o n was supplemented by m i x i n g s h e p h e r d ' s - p u r s e , l a m b ' s - q u a r t e r s and c h i c k w e e d s e e d s w i t h sand and b r o a d c a s t i n g t h e m i x t u r e o v e r t h e t o t a l p l o t a r e a . The seeds -44-were t h e n l i g h t l y r a k e d i n t o t h e s o i l w h i c h was t h e n p a c k e d u s i n g a r o l l e r . The c r o p s e e d l i n g s were t h i n n e d t o an i n t e r - p l a n t s p a c i n g o f 30 cm f o r b r o c c o l i and 3 t o 5 cm f o r o n i o n . A C0 2 s p r a y e r (138 kPa) w i t h a b r a s s , f l a t f a n n o z z l e ( T e e j e t 8003) was used t o a p p l y t h e ammonium n i t r a t e (800 L ha" 1; 0, 7.5, 10, 15, and 20 p e r c e n t N) 27 d a y s a f t e r s e e d i n g . The number o f weed s e e d l i n g s i n a 0.25 m2 a r e a was c o u n t e d b e f o r e s p r a y i n g . A t d i f f e r e n t d a t e s a f t e r s p r a y i n g , weeds v i s u a l l y e s t i m a t e d t o have 20 p e r c e n t o r more o f t h e i r l e a f and stem a r e a s t i l l g r e e n were c o u n t e d as l i v e . The number o f l i v e p l a n t s p e r m2 was c a l c u l a t e d . The e x p e r i m e n t was r e p e a t e d i n 1989, b u t no c r o p o r weed se e d s were p l a n t e d . F e r t i l i z e r l e v e l s were 97, 356, and 247 kg h a - 1 N, P, K r e s p e c t i v e l y . S o i l pH was 5.4 and, t h e r e f o r e , 5.7 t h a - 1 o f a f i n e mesh d o l o m i t e l i m e was a p p l i e d . The f e r t i l i z e r and l i m e were d i s k e d i n t o t h e s o i l on 6 J u l y 1989. T h e r e a f t e r t h e p l o t s were l e f t u n d i s t u r b e d and weeds f r o m t h e n a t u r a l p o p u l a t i o n were a l l o w e d t o emerge and grow. Twen t y - n i n e days a f t e r c u l t i v a t i o n t h e ammonium n i t r a t e was a p p l i e d . To d e t e r m i n e i f weed d e n s i t i e s p e r p l o t were e q u a l b e f o r e a p p l y i n g t h e ammonium n i t r a t e , t o t a l weed d e n s i t y a n d d e n s i t i e s o f e a c h i n d i v i d u a l weed s p e c i e s were f i t t e d t o t h e model: d0= b , + b , c o (3) 0 1 2 0 v ' w h e r e d o = weed d e n s i t y , c = c o n c e n t r a t i o n o f ammonium n i t r a t e ( p e r c e n t N) t o be a p p l i e d , b = weed d e n s i t y o f p l o t s t h a t w i l l r e c i e v e no ammonium n i t r a t e , and b 2 = t h e s l o p e . I f t h e s l o p e , b 2, does not d i f f e r (p>0.05) from 0, i t i n d i c a t e s t h a t t h e weed d e n s i t i e s were equal b e f o r e a p p l i c a t i o n o f t h e ammonium n i t r a t e . ( T h i s i s e q u i v a l e n t t o a -45-1-way ANOVA t o c o n f i r m t h a t t h e r e a r e no d i f f e r e n c e s i n t h e o r i g i n a l weed d e n s i t i e s ) . T o t a l weed d e n s i t y and t h e d e n s i t i e s o f e a c h i n d i v i d u a l weed s p e c i e s a f t e r ammonium n i t r a t e a p p l i c a t i o n were f i t t e d t o t h e model: d =a +a c (4) a 1 2 a v ' where d = weed d e n s i t y , c = ammonium n i t r a t e ( p e r c e n t N), a = weed a a 1 d e n s i t y when no ammonium n i t r a t e i s a p p l i e d , and a 2 = t h e s l o p e . The r e g r e s s i o n e q u a t i o n s f o r e a c h y e a r ( A p p e n d i x 1 and 2) were used t o c a l c u l a t e p e r c e n t weed c o n t r o l as a f u n c t i o n o f ammonium n i t r a t e c o n c e n t r a t i o n ( p e r c e n t N) ( F i g . 5 and 6 ) : %WC = [ [ / b (cp- / a (c a ) ] / / b (c^-A0%]100 (5) w i t h (0<c^<20 and 0<ca<20). %WC = p e r c e n t weed c o n t r o l , c^  = as above, c^  = as above, /b(c^) = r e g r e s s i o n e q u a t i o n ( 3 ) , / a ( c a ) = r e g r e s s i o n e q u a t i o n ( 4 ) , and A0% = L7 b(^)-/ a(c a)]// b(c^ (c^=0 and Cft=0). Shepherd's-purse Density and Weed Control. The f i e l d r e c e i v e d 69, 188, and 130 kg h a - 1 N, P, K r e s p e c t i v e l y i n 1987, and 54, 96, and 66 N, P, K r e s p e c t i v e l y i n 1988. S o i l pH was 6.2 i n 1987. In 1988 t h e pH was 5.4 and, t h e r e f o r e , 3.3 t ha" 1 o f l i m e was a p p l i e d . The n a t u r a l weed p o p u l a t i o n was c o n t r o l l e d w i t h a p r e p l a n t t r e a t m e n t o f t h e s o i l f u m i g a n t dazomet ( B a s a m i d ) , w h i c h was a p p l i e d a t a r a t e o f 3.81 kg 100 r r f 2 i n 1987 and 3.25 kg 100 n f 2 i n 1988. The fu m i g a n t was d i s k e d i n t o t h e s o i l and t h e s u r f a c e was s e a l e d u s i n g a p a c k e r . A f t e r 2 t o 3 weeks t h e s o i l was r o t o t i l l e d t o r e l e a s e t h e s t e r i l a n t fumes. I m m e d i a t e l y a f t e r t h e b r o c c o l i had been d i r e c t seeded i n a row -46-down t h e m i d d l e o f a p l o t , t h e s h e p h e r d ' s - p u r s e seed was mixed w i t h sand and b r o a d c a s t o v e r t h e t o t a l p l o t a r e a (1 m x 5 m). The weed seeds were l i g h t l y r a k e d i n t o t h e s o i l w h i c h was t h e n packed u s i n g a r o l l e r . A l l weeds e x c e p t s h e p h e r d ' s - p u r s e were removed by hand. The p l a n t i n g d a t e s were 23 J u n e 1987 and 7 J u l y 1988. The ammonium n i t r a t e s o l u t i o n (800 L ha" 1; 20 p e r c e n t N) was s p r a y e d as above on 15 J u l y 1987 (22 days a f t e r s e e d i n g ) and 2 August 1988 (26 days a f t e r s e e d i n g ) . C o n t r o l p l o t s had ammonium n i t r a t e (800 L h a - 1 ; 20 p e r c e n t N) s p r a y e d on t h e s o i l i n two bands on e i t h e r s i d e o f t h e c r o p . S h e p h e r d ' s - p u r s e d e n s i t i e s ( a s above) were measured b e f o r e and a f t e r s p r a y i n g . B r o c c o l i p l a n t s were t h i n n e d and h a r v e s t e d f o r s h o o t d r y w e i g h t d a t a as t h e season p r o g r e s s e d . The s h o o t d r y w e i g h t samples were t a k e n a t w e e k l y i n t e r v a l s s t a r t i n g j u s t b e f o r e ammonium n i t r a t e a p p l i c a t i o n and c u l m i n a t e d when t h e f l o w e r buds begun t o f o r m . The f i n a l s p a c i n g o f b r o c c o l i p l a n t s t h a t d e v e l o p e d m a t u r e h e a d s was a p p r o x i m a t e l y 30 t o 50 cm. Mature b r o c c o l i heads, c u t t o 20 cm l e n g t h s , were h a r v e s t e d t o d e t e r m i n e m a r k e t a b l e ( h e a d s >10 cm a c r o s s ) y i e l d s . The number o f heads h a r v e s t e d p e r p l o t was r e c o r d e d and a v e r a g e head w e i g h t s were c a l c u l a t e d . S h e p h e r d ' s - p u r s e d e n s i t i e s a f t e r ammonium n i t r a t e a p p l i c a t i o n were f i t t e d t o t h e model: d f=n(d.) (6) where d f= s h e p h e r d ' s - p u r s e d e n s i t y a f t e r ammonium n i t r a t e a p p l i c a t i o n , d. = s h e p h e r d ' s - p u r s e d e n s i t y b e f o r e ammonium n i t r a t e a p p l i c a t i o n , and n = t h e s l o p e . R e g r e s s i o n e q u a t i o n s (Appendix 3) were used t o c a l c u l a t e p e r c e n t weed c o n t r o l (Appendix 3 ) : -47-%SPC = [( d . - / ( d . ) ) / d . ] 1 0 0 (7) w i t h (52<d.<656) i n 1987 and (256<d.<988) i n 1988. %SPC = p e r c e n t s h e p h e r d ' s - p u r s e c o n t r o l , /(d.) = r e g r e s s i o n e q u a t i o n ( 6 ) , and d. = as above. B r o c c o l i d r y w e i g h t s , y i e l d , and average head w e i g h t were f i t t e d t o t h e model: y=q 1+q 2d i (8) where y = d r y w e i g h t , y i e l d , o r average head w e i g h t , d. = as above, q i = weed f r e e d r y w e i g h t , y i e l d , o r average head w e i g h t , and q 2 = t h e s l o p e (Appendix 4 ) . ( i i ) R e s u l t s and D i s c u s s i o n Relative Susceptibilitv of Weed Species. Weed s p e c i e s c a n be c l a s s i f i e d i n t o t h r e e g e n e r a l g r o u p s : (1) s u s c e p t i b l e - t h o s e whose d e n s i t i e s were s i g n i f i c a n t l y (p<0.05) d e c r e a s e d by t h e ammonium n i t r a t e a p p l i c a t i o n s ( s h e p h e r d ' s - p u r s e , c h i c k w e e d , c u d w e e d , and r e d r o o t p i g w e e d ) , ( 2 ) p a r t i a l l y s u s c e p t i b l e - t h o s e whose d e n s i t i e s w e r e i n i t i a l l y u n a f f e c t e d , but l a t e r d e c r e a s e d s i g n i f i c a n t l y ( c o r n s p u r r y i n 1989), and (3) t o l e r a n t - t h o s e whose d e n s i t i e s were not s i g n i f i c a n t l y a f f e c t e d ( l a m b ' s - q u a r t e r s , p u r s l a n e , c o r n s p u r r y ( i n 1987) and annual b l u e g r a s s ) ( A p p e n d i x 1 and 2; F i g . 5 and 6 ) . I n a d d i t i o n , f i e l d o b s e r v a t i o n s i n d i c a t e d t h a t t h e f o l i a g e o f l a d y ' s - t h u m b (Polygonum persicaria) and common g r o u n d s e l (Senecio vulgaris) i s s e v e r e l y b u r n t by th e ammonium n i t r a t e s p r a y ( F i g . 7 ) . Under C a l i f o r n i a c o n d i t i o n s s h e p h e r d ' s - p u r s e , c h i c k w e e d , r e d r o o t p i g w e e d , and common g r o u n d s e l were r e p o r t e d t o be s u s c e p t i b l e t o ammonium n i t r a t e b u r n i n g ( A g a m a l i a n 1 9 8 8 ) . A summary o f 13 f i e l d -48-F i g . 5. P e r c e n t weed c o n t r o l i n 1987 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s ( p e r c e n t N) a t (A,B) 2 and (C,D) and an ave r a g e o f 46 days a f t e r a p p l i c a t i o n . (A,C) Weed s p e c i e s w h i c h were s i g n i f i c a n t l y a f f e c t e d by t h e ammonium n i t r a t e t r e a t m e n t s and (B,D) t h o s e w h i c h w e r e n o t ( A p p e n d i x 1 ) . P e r c e n t weed c o n t r o l (%WC) was c a l c u l a t e d u s i n g t h e r e g r e s s i o n e q u a t i o n s f r o m A p p e n d i x 1 as d e s c r i b e d i n t h e t e x t ( E q u a t i o n 5 on p . 4 5 ) . In t h e c a s e o f r e d r o o t pigweed, %WC was g r e a t e r t h a n 100 p e r c e n t f o r 19.0 t o 20.0 p e r c e n t N a t day 2 and 19.3 t o 20.0 p e r c e n t N a t day 46. Because i t i s b i o l o g i c a l l y i m p o s s i b l e t o have more t h a n 100 p e r c e n t weed c o n t r o l t h e s e v a l u e s were n o t p l o t t e d . F i g . 5 AMMONIUM NITRATE CONCENTRATION (PERCENT N) -50-F i g . 6. P e r c e n t weed c o n t r o l i n 1989 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s ( p e r c e n t N) a t (A) 4 and (B) 12 days a f t e r a p p l i c a t i o n . P e r c e n t weed c o n t r o l (%WC) was c a l c u l a t e d u s i n g t h e r e g r e s s i o n e q u a t i o n s from A p p e n d i x 2 as d e s c r i b e d i n t h e t e x t ( E q u a t i o n 5 on p . 4 5 ) . I n t h e c a s e o f s h e p h e r d ' s - p u r s e , %WC was g r e a t e r t h a n 100 p e r c e n t f o r 16.6 t o 20.0 p e r c e n t N a t day 4 and 19.1 t o 20.0 p e r c e n t N a t day 12. Because i t i s b i o l o g i c a l l y i m p o s s i b l e t o have more t h a n 100 p e r c e n t weed c o n t r o l t h e s e v a l u e s were not p l o t t e d . -51-F i g . 6 o cc 1 2 0 1 0 0 8 0 6 0 4 0 2 0 0 O O Q - 2 0 L U L U L U o C C L U C L -A shepherd's-purse /cudweed yS y/ cornspurry lamb's-quarters I I I I 0 - 2 0 10 15 2 0 2 5 shepherd's-purse cornspurry cudweed lamb's-quarters 0 5 10 15 2 0 2 5 A M M O N I U M N I T R A T E C O N C E N T R A T I O N ( P E R C E N T N) -52-F i g . 7. S u s c e p t i b l e and t o l e r a n t weed s p e c i e s 2 days a f t e r ammonium n i t r a t e ( 2 0 p e r c e n t N) a p p l i c a t i o n . S u s c e p t i b l e weeds i n c l u d e (SP) s h e p h e r d ' s - p u r s e , (CW) c u d w e e d y (RRP) r e d r o o t p i g w e e d , ( L T ) 1 a d y ' s - t h u m b , and (GR) common g r o u n d s e l . P a r t i a l l y s u s c e p t i b l e (CSP) c o r n s p u r r y . T o l e r a n t weeds i n c l u d e ( L Q ) l a m b ' s - q u a r t e r s a n d ( P L ) p u r s l a n e . ( B a r = 15 cm). -53--54-e x p e r i m e n t s i n d i c a t e d t h a t s h e p h e r d ' s - p u r s e , c h i c k w e e d , r e d r o o t pigweed, and common g r o u n d s e l w e r e c o n t r o l l e d 9 5 , 9 7 , 9 6 , and 98 p e r c e n t r e s p e c t i v e l y a t t h e o n e - t o - f o u r t r u e l e a f s t a g e and 41, 51, 58, and 68 p e r c e n t r e s p e c t i v e l y a t t h e f i v e - t o - s e v e n t r u e l e a f s t a g e ( A g a m a l i a n 1988). L a m b ' s - q u a r t e r s , p u r s l a n e , and annual b l u e g r a s s were r e p o r t e d as r e s i s t a n t w i t h no c o n t r o l a t both l e a f s t a g e s ( A g a m a l i a n 1988). The r e s u l t s c l e a r l y i n d i c a t e t h a t s u s c e p t i b l e s p e c i e s a r e more e f f e c t i v e l y c o n t r o l l e d a t t h e h i g h e r ammonium n i t r a t e c o n c e n t r a t i o n s . T h i s was p a r t i c u l a r l y t r u e f o r t h e r e d r o o t pigweed ( F i g . 5A and 5C) and s h e p h e r d ' s - p u r s e ( F i g 6A and 6 B ) . However, t h e r e i s l i k e l y t o be a p o i n t where i n c r e a s i n g c o n c e n t r a t i o n s o f ammonium n i t r a t e w i l l n o t p r o v i d e a d d i t i o n a l weed k i l l . The r e s u l t s a l s o show a l a r g e p e r c e n t i n c r e a s e i n annual b l u e g r a s s a t an a v e r a g e o f 46 days a f t e r ammonium n i t r a t e a p p l i c a t i o n ( F i g . 5D). Whether t h i s i n c r e a s e , w h i c h r e p r e s e n t s a s t a t i s t i c a l l y i n s i g n i f i c a n t (p<0.05) change i n weed d e n s i t y ( o f 10 p l a n t s n f 2 ) , i s a consequence o f t h e ammonium n i t r a t e a p p l i c a t i o n r e m a i n s t o be d e t e r m i n e d . A l t h o u g h o v e r a l l weed c o n t r o l i n 1987 was g r e a t e r t h a n 70 p e r c e n t , t h e r e m a i n i n g weeds e a s i l y p r e v e n t e d b o t h c r o p s ( b r o c c o l i and o n i o n ) from a t t a i n i n g a m a r k e t a b l e s i z e ( d a t a not shown). A number o f f a c t o r s may be r e s p o n s i b l e f o r c r o p f a i l u r e . F i r s t , t h e i n i t i a l weed d e n s i t y was v e r y h i g h (799 p l a n t s m~2) (Appendix 1 ) . T h i s may have p r e v e n t e d good s p r a y c o v e r a g e o f t h e f e r t i l i z e r on t h e f o l i a g e o f t h e weeds. Second, a l a r g e number o f r e s i s t a n t weed s p e c i e s were p r e s e n t and t h e s e p l a n t s were n o t a f f e c t e d by t h e ammonium n i t r a t e s p r a y . They c o n t i n u e d t o grow and compete w i t h t h e c r o p . T h i r d , even t h e s u s c e p t i b l e weeds t h a t were s e v e r e l y b u r n t , c o u l d , i n t i m e , r e c o v e r and b e g i n t o compete -55-w i t h t h e c r o p . The above f i n d i n g s i n d i c a t e t h a t good weed c o n t r o l by ammonium n i t r a t e w i l l depend on a number o f key f a c t o r s . F i r s t , t h e a v a i l a b l e p r e - e m e r g e n t h e r b i c i d e s ( t r i f l u r a l i n and DCPA) mus t be u s e d t o e f f e c t i v e l y c o n t r o l weeds r e s i s t a n t t o ammonium n i t r a t e . F o r t u n a t e l y g r a s s y s p e c i e s , l a m b ' s - q u a r t e r s , and p u r s l a n e a r e c o n t r o l l e d by t h e s e h e r b i c i d e s . Second, good s p r a y c o v e r a g e i s e s s e n t i a l . Weed d e n s i t y s h o u l d n o t be t o o g r e a t n o r t h e p l a n t s t o o l a r g e ( r e l a t e d t o weed a g e ) , o t h e r w i s e t h e weed f o l i a g e w i l l o v e r l a p and p r e v e n t c o m p l e t e s p r a y c o v e r a g e . T h i r d , s u s c e p t i b l e s p e c i e s must be b u r n t back f a r enough t h a t even i f t h e y do r e c o v e r t h e y w i l l n ot e f f e c t i v e l y compete w i t h t h e c r o p . C o n t r o l o f s u s c e p t i b l e s p e c i e s c o u l d be i n c r e a s e d by a s e c o n d a p p l i c a t i o n o f ammonium n i t r a t e o r h i l l i n g ( s o i l pushed up t o t h e seed l i n e ) t o b u r y any weeds t h a t m ight not have b e e n . k i l l e d ( N a e g e r l y 1985). Shepherd's-purse density and weed control. S h e p h e r d ' s - p u r s e d e n s i t i e s were e f f e c t i v e l y r e d u c e d by t h e ammonium n i t r a t e (800 L h a - 1 ; 20 p e r c e n t N) ( F i g . 8 and 9 ) . Two d a y s a f t e r ammonium n i t r a t e a p p l i c a t i o n , 92 p e r c e n t ( 1 9 8 7 ) a n d 85 p e r c e n t ( 1 9 8 8 ) o f t h e s h e p h e r d ' s - p u r s e p l a n t s were dead ( A p p e n d i x 3 ) . F o u r t e e n (1987) t o f i f t e e n (1988) days a f t e r a p p l i c a t i o n t h e s e r a n g e s were 90 p e r c e n t and 76 p e r c e n t r e s p e c t i v e l y . A f t e r 22 days (1988) weed k i l l was 78 p e r c e n t . The o b s e r v e d d e c r e a s e i n weed c o n t r o l f r o m two da y s a f t e r t o two t o t h r e e weeks a f t e r s p r a y i n g may have o c c u r r e d f o r two r e a s o n s . F i r s t , new p l a n t s may have emerged and been r e c r u i t e d t o t h e p l a n t p o p u l a t i o n . Second, p l a n t s w h i c h were i n i t i a l l y c o u n t e d as dead (80 p e r c e n t o r more o f t h e i r f o l i a g e b u r n t ) may have r e c o v e r e d ( F i g . 1 0 ) . -56-F i g . 8. The e f f e c t o f s h e p h e r d ' s - p u r s e d e n s i t y on i t s c o n t r o l by ammonium n i t r a t e (20 p e r c e n t N ) : (A) 1987 and (B) 1988. Days a f t e r ammonium n i t r a t e a p p l i c a t i o n a r e i n d i c a t e d on t h e g r a p h . See App e n d i x 3 f o r a n a l y s i s . -57-F i g . 8 c o -4—/ c Q. LU GO CC CL I CO Q CC-LU X CL LU X GO LL o cc LU CD Z ) < 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0 1 1 0 0 0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0 1 1 0 0 I N I T I A L N U M B E R O F S H E P H E R D ' S - P U R S E (plants m"2) -58-F i g . 9. S h e p h e r d ' s - p u r s e c o n t r o l by ammonium n i t r a t e (20 p e r c e n t N): ( a ) b e f o r e and ( b ) a f t e r ammonium n i t r a t e a p p l i c a t i o n . Ammonium n i t r a t e s e l e c t i v e l y c o n t r o l l e d s h e p h e r d ' s - p u r s e i n b r o c c o l i ( c v . Emperor). Weed l e a v e s w i l t e d w i t h i n m i n u t e s o f t r e a t m e n t and a l m o s t a l l p l a n t s t u r n e d c o m p l e t e l y brown w i t h i n 24 h r . \ -59--60-F i g . 10. A s m a l l p e r c e n t a g e o f s h e p h e r d ' s - p u r s e p l a n t s , w h i c h were n o t c o m p l e t e l y b u r n t , resumed g r o w t h and r e c o v e r e d . T h i s s u g g e s t s t h a t an a d d i t i o n a l a p p l i c a t i o n o f ammonium n i t r a t e may be n e c e s s a r y . ( B a r = 15 cm). -61--62-P e r c e n t weed c o n t r o l i n 1988 was l o w e r t h a n 1987; s e v e n p e r c e n t l e s s a t two days a f t e r ammonium n i t r a t e a p p l i c a t i o n and 14 p e r c e n t l e s s a t 2 weeks. T h i s may have o c c u r r e d because t h e 1988 p l a n t s were f o u r d a y s o l d e r a t t h e t i m e o f s p r a y i n g t h a n t h e 1987 p l a n t s . As n o t e d p r e v i o u s l y , a t t h e o n e - t o - f o u r t r u e l e a f s t a g e s h e p h e r d ' s - p u r s e was c o n t r o l l e d 54 p e r c e n t more t h a n a t t h e f i v e - t o - s e v e n t r u e l e a f s t a g e ( A g a m a l i a n 1988). A l t h o u g h f o u r days does n o t appear t o be a l a r g e t i m e d i f f e r e n c e , i t may have a l l o w e d t h e 1988 p l a n t s enough t i m e t o i n c r e a s e t h e i r s i z e t o a c c o u n t f o r t h e l o w e r p e r c e n t weed c o n t r o l . In a d d i t i o n , a f t e r two weeks more p l a n t s i n 1988 had r e c o v e r e d from t h e i n i t i a l weed c o n t r o l t h a n i n 1987; 9 p e r c e n t (1988) compared t o 2 p e r c e n t ( 1 9 8 7 ) . In p a r t t h i s may be due t o t h e l a r g e r weed d e n s i t i e s i n 1988 (256 t o 988 p l a n t s m"2 compared t o 52 t o 656 p l a n t s n f 2 ) . Large d e n s i t i e s s u g g e s t an o v e r l a p p i n g o f l e a v e s and, t h e r e f o r e , l e s s c o m p l e t e s p r a y c o v e r a g e and p l a n t d e a t h . S i m i l a r l y , i f t h e weeds were s l i g h t l y l a r g e r i n 1988, t h e r e may a l s o have been an o v e r l a p p i n g o f t h e b a s a l , r o s e t t e l e a v e s . T h i s t o o would c o n t r i b u t e t o i n c o m p l e t e s p r a y c o v e r a g e and p l a n t d e a t h . The s u r v i v i n g s h e p h e r d ' s - p u r s e p l a n t s d i d n o t s i g n i f i c a n t l y (p<0.05) a f f e c t b r o c c o l i y i e l d and a v e r a g e head w e i g h t ( A p p e n d i x 4 ) . Nor d i d t h e y a f f e c t c r o p growth e x c e p t i n 1988 a t 21 days a f t e r ammonium n i t r a t e a p p l i c a t i o n (p=0.03) (Appendix 4 ) . T h i s i s somewhat un e x p e c t e d because t h e l a r g e s t d e n s i t i e s o f s h e p h e r d ' s - p u r s e p l a n t s s u r v i v i n g i n 1988 ranged from 149 (day 2) t o 219 (day 15) p l a n t s n f 2 , a l a r g e number o f weeds. However, a l l t h e p l a n t s c o u n t e d as l i v e had s u f f e r e d some l e a f damage w h i c h p r o b a b l y r e d u c e d t h e i r c o m p e t i t i v e a b i l i t y . In a d d i t i o n , s h e p h e r d ' s - p u r s e w i t h i t s b a s a l r o s e t t e o f l e a v e s , s h o r t -63-f l o w e r i n g s t a l k , and l i m i t e d r o o t s y s t e m w o u l d n o t be e x p e c t e d t o compete s t r o n g l y a g a i n s t t h e b r o c c o l i . Indeed, i n t r i f l u r a l i n - t r e a t e d p l o t s w i t h a weed p o p u l a t i o n c o n s i s t i n g m a i n l y o f s h e p h e r d ' s - p u r s e , f a l l t r a n s p l a n t e d cabbage competed so w e l l w i t h t h e s h e p h e r d ' s - p u r s e t h a t i t r e d u c e d weed w e i g h t and had few e r weeds t h a n t h e c r o p f r e e p l o t s (Lawson 1972). In a d d i t i o n , t h e r e was no l o s s i n cabbage y i e l d (Lawson 1972). The above f i n d i n g s c l e a r l y d e m o n s t r a t e t h a t ammonium n i t r a t e can e f f e c t i v e l y be used t o c o n t r o l v e r y h i g h d e n s i t i e s o f s h e p h e r d ' s - p u r s e , t h e major p r o b l e m i n t r i f l u r a l i n t r e a t e d b r o c c o l i f i e l d s , w i t h l i t t l e o r no d e c r e a s e i n c r o p growth and y i e l d . 4.3 R e l a t i v e S u s c e p t i b i l i t y o f C o l e and Onion C u l t i v a r s ( i ) M a t e r i a l s and Methods F i e l d e x p e r i m e n t s were c o n d u c t e d a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a P l a n t S c i e n c e F i e l d L a b o r a t o r y i n 1987 and 1988. S o i l ( B ose, sandy loam w i t h 6.6 p e r c e n t o r g a n i c m a t t e r ) s a m p l e s were t e s t e d each s p r i n g t o d e t e r m i n e n u t r i e n t s t a t u s and pH. The f i e l d r e c e i v e d 89, 212, and 147 kg ha" 1 N, P, K r e s p e c t i v e l y i n 1987 and 54, 96, and 66 kg h a - 1 N, P, K r e s p e c t i v e l y i n 1988. S o i l pH was 6.2 i n 1987, but i n 1988 t h e pH was 5.5 so 3.3 t ha" 1 o f a f i n e mesh d o l o m i t e ( r a t e d e t e r m i n e d as b e f o r e ) was a p p l i e d . A s p l i t p l o t d e s i g n w i t h ammonium n i t r a t e ( s o l u t i o n d e s c r i b e d p r e v i o u s l y on p. 43) as t h e main p l o t e f f e c t , and c u l t i v a r s as t h e s u b p l o t e f f e c t , and f o u r b l o c k s p e r t r e a t m e n t was used. B r o c c o l i ( c v s . E m p e r o r , S G I ) , B r u s s e l s s p r o u t s ( c v . L u n e t ) , cabbage ( c v . E a r l y M a r v e l ) , c a u l i f l o w e r ( c v s . E l g o n , M a t r a ) , and o n i o n ( c v . W h i t e L i s b o n ) were d i r e c t s eeded as d e s c r i b e d p r e v i o u s l y . The -64-i n t e r - p l a n t s p a c i n g was 30 cm f o r b r o c c o l i and c a b b a g e , 46 cm f o r c a u l i f l o w e r and B r u s s e l s s p r o u t s , and a p p r o x i m a t e l y 3 t o 5 cm f o r o n i o n . The p l a n t i n g d a t e s were 4 June 1987 and 8 June 1988. P l o t s were k e p t weed f r e e by hand weeding. Ammonium n i t r a t e (800 L h a - 1 ; 0, 10, 15, and 20 p e r c e n t N) was s p r a y e d 26 days a f t e r s e e d i n g i n 1987 and 38 t o 39 days a f t e r s e e d i n g i n 1988. Ammonium n i t r a t e (20-0-0) was a l s o s p r a y e d on t h e s o i l i n two bands on e i t h e r s i d e o f t h e c r o p a t r a t e s o f 800, 4 0 0 , a n d 200 L h a " 1 f o r t h e 0, 10, and 15 p e r c e n t N t r e a t m e n t s r e s p e c t i v e l y . T h e r e f o r e , a l l p l o t s r e c e i v e d t h e same t o t a l amount o f n i t r o g e n ( 1 6 0 kg h a - 1 ) . S h o o t d r y w e i g h t s w e r e t a k e n a t w e e k l y i n t e r v a l s s t a r t i n g from t h e day o f s p r a y i n g . The s a m p l i n g c u l m i n a t e d when t h e f l o w e r buds began t o form. Y i e l d s were measured, t h e number o f p l a n t s p e r p l o t was r e c o r d e d , and t h e y i e l d p e r p l a n t was c a l c u l a t e d . The i n s e c t i c i d e d i a z i n o n ( B a s u d i n ) ( t o c o n t r o l r o o t maggots), t h e f u n g i c i d e s c a p t a n ( C a p t a n ) and c h l o r o t h a l o n i l ( B r a v o ) ( t o c o n t r o l damping o f f ) , and t h e f e r t i l i z e r s b o r i c a c i d and Epsom s a l t s ( f o l i a r s p r a y ) ( t o p r e v e n t h o l l o w stem) were a p p l i e d as n e c e s s a r y . B r o c c o l i , c a b b a g e , c a u l i f l o w e r , and o n i o n s were h a r v e s t e d between A u g u s t and September, and B r u s s e l s s p r o u t s between O c t o b e r and November. P l a n t d r y w e i g h t s were f i t t e d t o t h e model: l o g ( y ) = r L + r 2 x + r 3 x 2 (9) where y = p l a n t d r y w e i g h t , x = t i m e i n d a y s a f t e r ammonium n i t r a t e a p p l i c a t i o n , r = i n i t i a l d r y w e i g h t b e f o r e ammonium n i t r a t e a p p l i c a t i o n , and r 2 and r 3 = s l o p e c o n s t a n t s . I f r 3 was i n s i g n i f i c a n t -65-(p<0.05) t h e n t h e d a t a were f i t t e d t o t h e model: l o g ( y ) = r : + r 2 x (10) where a l l t h e v a r i a b l e s = as above. R e g r e s s i o n e q u a t i o n s ( A p p e n d i x 5 and 6) were used t o c a l c u l a t e p e r c e n t r e l a t i v e growth f o r 10, 15, and 20 p e r c e n t N ( F i g s . 11 t o 14 ) : %RG = [ [ [ f ( x )+k ] - LT (x)+k]]/ | /(x)+k] -A0%]100 (11) an c c w i t h (0<x<28) i n 1987 and (0<x<14) i n 1988. %RG = p e r c e n t r e l a t i v e g r o w t h , x = as above, / c ( x ) = r e g r e s s i o n e q u a t i o n d e s c r i b i n g l o g d r y m a t t e r a c c u m u l a t i o n f o r 0 p e r c e n t N, / ( x ) = r e g r e s s i o n e q u a t i o n d e s c r i b i n g l o g d r y m a t t e r a c c u m u l a t i o n f o r 10, 15 and 20 p e r c e n t N, A0% = [L/ a n(x)+k]-|/(x)+k]]/r/ r(x)+k] (x=0), and k = l - f ( x = 0 ) . an c c c C r o p y i e l d s p e r p l o t and p e r p l a n t were f i t t e d t o t h e model: y = s ^ c (12) w h e r e y = y i e l d p e r p l o t o r p e r p l a n t , and c = ammonium n i t r a t e c o n c e n t r a t i o n ( p e r c e n t N ) , s i = y i e l d p e r p l o t o r p e r p l a n t when no ammonium n i t r a t e was a p p l i e d , and s ? = t h e s l o p e (Appendix 7 and 8 ) . ( i i ) R e s u l t s and D i s c u s s i o n Crop g r o w t h r a t e s were more a d v e r s e l y a f f e c t e d by t h e ammonium n i t r a t e s p r a y i n 1987 than 1988. F o r example, i n 1987 t h e f i r s t 14 days a f t e r ammonium n i t r a t e a p p l i c a t i o n saw a r e t a r d a t i o n i n t h e p e r c e n t r e l a t i v e g r o w t h o f N S G I ' ( b r o c c o l i ) and ' L u n e t ' ( B r u s s e l s s p r o u t s ) ( F i g . 1 1 ) . In 1988 t h e r e was e i t h e r no e f f e c t o r an i n c r e a s e i n p e r c e n t r e l a t i v e growth f o r t h e s e two c u l t i v a r s ( F i g . 1 2 ) . In a d d i t i o n , 'Matra' ( c a u l i f l o w e r ) and x E l g o n ' ( c a u l i f l o w e r ) had a much l a r g e r r e t a r d a t i o n o f p l a n t growth r a t e s i n 1987 compared t o 1988 ( F i g . 11 and 12 ) . -66-F i g . 11. P e r c e n t r e l a t i v e g r o w t h f o r V S G 1 ' ( b r o c c o l i ) , x L u n e t ' ( B r u s s e l s s p r o u t s ) , v M a t r a ' ( c a u l i f l o w e r ) , and ' E l g o n ' ( c a u l i f l o w e r ) i n 1987 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s : ( ) 10, ("') 15, and (---) 20 p e r c e n t N. P o i n t s on graph i n d i c a t e A0% ( E q u a t i o n 11 d e s c r i b e d on p.65) f o r ( O ) 10, (•) 15, and (A) 20 p e r c e n t N. P e r c e n t r e l a t i v e g rowth (%RG) was c a l c u l a t e d u s i n g r e g r e s s i o n e q u a t i o n s from A p p e n d i x 5 ( E q u a t i o n 11 d e s c r i b e d on p . 6 5 ) . F i g . 11 8 10 12 14 16 18 20 22 24 26 28 30 6 8 10 12 14 16 18 20 22 24 26 28 30 L U N E T 6 8 10 12 14 16 18 20 22 24 26 28 30 40 30 20 10 0 -10 -20 -30 -40 E L G O N _i i i i_ 6 8 10 12 14 16 18 20 22 24 26 28 30 D A Y S A F T E R A M M O N I U M N I T R A T E A P P L I C A T I O N -68-F i g . 12. P e r c e n t r e l a t i v e g r o w t h f o r ' S G I ' ( b r o c c o l i ) , ' L u n e t ' ( B r u s s e l s s p r o u t s ) , ' M a t r a ' ( c a u l i f l o w e r ) , and ' E l g o n ' ( c a u l i f l o w e r ) i n 1988 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s : ( ) 10, (*") 15, and (---) 20 p e r c e n t N. P o i n t s on graph i n d i c a t e A0% ( E q u a t i o n 11 d e s c r i b e d on p. 65) f o r ( O ) 10, (•) 15, and (A) 20 p e r c e n t N. P e r c e n t r e l a t i v e g r o w t h (%RG) was c a l c u l a t e d u s i n g r e g r e s s i o n e q u a t i o n s from Appendix 6 ( E q u a t i o n 11 d e s c r i b e d on p . 6 5 ) : F i g . 12 - E L G O N i i i i i I I i I I 1 0 1 2 1 4 16 D A Y S - A F T E R A M M O N I U M N I T R A T E A P P L I C A T I O N -70-The o b s e r v e d d i f f e r e n c e s i n p e r c e n t r e l a t i v e g r o w t h i n t h e two g r o w i n g seasons may be l i n k e d t o d i f f e r e n c e s i n c r o p age a t t h e t i m e o f s p r a y i n g . In 1987 t h e p l a n t s were a t t h e 2 t o 3 t r u e l e a f s t a g e (26 d a y s a f t e r s e e d i n g ) w h i l e i n 1988 p l a n t s were a t t h e 6 t o 8 t r u e l e a f s t a g e (38 t o 39 days a f t e r s e e d i n g ) . A g a m a l i a n (1988) f o u n d t h a t t h e damage s u f f e r e d by s u s c e p t i b l e weed s p e c i e s d i f f e r e d d e p e n d i n g on p l a n t a g e . P l a n t s a t t h e one t o f o u r t r u e l e a f s t a g e w e r e much more s u s c e p t i b l e t o f e r t i l i z e r b u r n i n g t h a n p l a n t s a t t h e f i v e t o seven t r u e l e a f s t a g e ( A g a m a l i a n 1988). D i f f e r e n c e s i n d r y m a t t e r a c c u m u l a t i o n can be u s e d t o compare c u l t i v a r t o l e r a n c e o r s u s c e p t i b i l i t y t o ammonium n i t r a t e . The two c a u l i f l o w e r c u l t i v a r s , ' M a tra' and ' E l g o n ' , a r e t h e most s u s c e p t i b l e t o ammonium n i t r a t e damage. B o t h had a l a r g e d e c r e a s e i n r a t e s o f d r y m a t t e r a c c u m u l a t i o n r e l a t i v e t o t h e o t h e r c u l t i v a r s , a l t h o u g h t h i s r e s p o n s e was more marked i n 1987. In a n o t h e r s t u d y ( A g a m a l i a n 1988) c a u l i f l o w e r was o b s e r v e d t o s u f f e r more f o l i a r damage t h e n b r o c c o l i and i n some i n s t a n c e s t h e g r o w i n g p o i n t was d e s t r o y e d , w h i c h r e s u l t e d i n d i s t o r t e d c u r d d e v e l o p m e n t . No d e s t r u c t i o n o f t h e g r o w i n g p o i n t o r e x c e s s i v e f o l i a g e burn was o b s e r v e d i n t h e s e e x p e r i m e n t s . However, a t t h e t i m e o f s p r a y i n g t h e l e a f a r e a o f ' M a t r a ' and ' E l g o n ' was much s m a l l e r t h a n t h a t o f t h e o t h e r c o l e c u l t i v a r s and, t h e r e f o r e , even a s m a l l amount o f f o l i a r damage may have had a major impact on c a u l i f l o w e r p h o t o s y n t h e s i s and g r o w t h . ' W h i t e L i s b o n ' ( o n i o n ) was t h e most r e s i s t a n t c u l t i v a r . I t s g r o w t h r a t e was e i t h e r n o t a f f e c t e d o r i n c r e a s e d s l i g h t l y w i t h t h e -71-ammonium n i t r a t e a p p l i c a t i o n s ( F i g . 13 and 1 4 ) . T h i s f i n d i n g c o n c u r s w i t h o t h e r o b s e r v a t i o n s s u c h as t h e a b i l i t y o f o n i o n t o t o l e r a t e s u l p h u r i c a c i d (used a t one t i m e t o c o n t r o l weeds i n o n i o n ) ( N a e g e r l y 1985) and ammonium s u l p h a t e (Cudney and O r l o f f 1988). The r e m a i n i n g c u l t i v a r s v a r i e d i n t h e i r t o l e r a n c e t o t h e ammonium n i t r a t e , a l t h o u g h a l l had some f o l i a r damage ( F i g . 1 5 ) . ' L u n e t ' ( B r u s s e l s s p r o u t s ) e x p e r i e n c e d a c o n s i d e r a b l e l o s s i n t h e r a t e o f d r y m a t t e r a c c u m u l a t i o n i n 1987, but n o t i n 1988 ( F i g . 11 and 1 2 ) . To a l e s s e r d e g r e e t h e same was t r u e f o r 'SGI' ( b r o c c o l i ) ( F i g . 11 and 1 2 ) . Growth r a t e s o f ' E a r l y M a r v e l ' (cabbage) and 'Emperor' ( b r o c c o l i ) were not a f f e c t e d i n 1987, but d e c r e a s e d a t 15 p e r c e n t N i n 1988 ( F i g . 13 and 1 4 ) . These d i f f e r e n c e s i n c u l t i v a r r e s p o n s e f o r t h e d i f f e r e n t g r o w i n g s e a s o n s make g e n e r a l i z a t i o n s about c u l t i v a r e f f e c t s d i f f i c u l t . However, ' L u n e t ' ( B r u s s e l s s p r o u t s ; 10, 1 5 , and 20 p e r c e n t N) and ' S G I ' ( b r o c c o l i ; 20 p e r c e n t N) had a g r e a t e r r e d u c t i o n i n t h e i r growth r a t e s a f t e r s p r a y i n g a t t h e t w o - t o - t h r e e l e a f s t a g e (1987) t h a n 'Emperor' ( b r o c c o l i ) and ' E a r l y M a r v e l ' ( c a b b a g e ) . T h e r e f o r e , 'Lunet' ( B r u s s e l s s p r o u t s ) and 'SGI' ( b r o c c o l i ) appear t o be more s u s c e p t i b l e t o ammonium n i t r a t e i n j u r y when t h e y a r e young ( F i g 11 and 1 3 ) . A l t h o u g h t h e g r o w t h r a t e s o f ' M a t r a ' ( c a u l i f l o w e r ) , ' E l g o n ' ( c a u l i f l o w e r ) , ' L u n e t ' ( B r u s s e l s s p r o u t s ) , and ' S G I ' ( b r o c c o l i ) i n i t i a l l y d e c r e a s e d ( e s p e c i a l l y i n 1987) most showed some s i g n s o f r e c o v e r i n g f r o m t h i s s e t b a c k ( F i g . 1 1 ) . G r o w t h r a t e s o f ' S G I ' ( b r o c c o l i ) f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s (10, 15, and 20 p e r c e n t N) w e r e t h e same as t h e c o n t r o l a t 14, 2 0 , and 28 d a y s r e s p e c t i v e l y a f t e r ammonium n i t r a t e a p p l i c a t i o n ( F i g . 1 1 ) . I n d e e d , -72-F i g . 13. P e r c e n t r e l a t i v e growth f o r x W h i t e L i s b o n ' ( o n i o n ) , N E a r l y M a r v e l ' ( c a b b a g e ) , and ' E m p e r o r ' ( b r o c c o l i ) i n 1987 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s : ( ) 10, ('"') 15, and ( — ) 20 p e r c e n t N. P o i n t s on g r a p h i n d i c a t e A0% ( E q u a t i o n 11 d e s c r i b e d on p.65) f o r ( O ) 10, (•) 15, and ( A ) 20 p e r c e n t N. P e r c e n t r e l a t i v e g r o w t h (%RG) was c a l c u l a t e d u s i n g r e g r e s s i o n e q u a t i o n s f r o m A p p e n d i x 5 ( E q u a t i o n 11 d e s c r i b e d on p . 6 5 ) . - 7 3 -F i g . 13 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 6 8 10 12 14 16 18 20 22 24 26 28 30 - E M P E R O R Q i i i i > i i i 6 8 10 12 14 16 18 20 22 24 26 28 30 D A Y S A F T E R A M M O N I U M N I T R A T E A P P L I C A T I O N -74-F i g . 14. P e r c e n t r e l a t i v e growth f o r 'White L i s b o n ' ( o n i o n ) , ' E a r l y M a r v e l ' ( c a b b a g e ) , and ' E m p e r o r ' ( b r o c c o l i ) i n 1988 f o r d i f f e r e n t ammonium n i t r a t e c o n c e n t r a t i o n s : ( ) 10, ('") 15, and (---) 20 p e r c e n t N. P o i n t s on g r a p h i n d i c a t e A0% ( E q u a t i o n 11 d e s c r i b e d on p.65) f o r ( O ) 10, (•) 15, and ( A ) 20 p e r c e n t N. P e r c e n t r e l a t i v e g r o w t h (%RG) was c a l c u l a t e d u s i n g r e g r e s s i o n e q u a t i o n s f r o m A p p e n d i x 6 ( E q u a t i o n 11 d e s c r i b e d on p. 6 5 ) . -75-F i g . 14 I" I— o cc CD LU > !< _ J LU CC L U O C C L U C L 4 0 30 20 10 0 -10 -20 -30 -40 40 30 20 10 0 -10 -20 -30 -40 W H I T E L I S B O N rf*^--— o . i i i i i 10 12 14 16 - E A R L Y M A R V E L - • 1 1 1 i i i i i 10 12 14 16 0 2 4 6 8 10 12 D A Y S A F T E R A M M O N I U M N I T R A T E A P P L I C A T I O N -76-F i g . 15. B r o c c o l i ( c v . Emperor) (a) 15 m i n u t e s and (b) 2 days a f t e r ammonium n i t r a t e (20 p e r c e n t N) a p p l i c a t i o n ( 1 9 8 8 ) . (a) The ammonium n i t r a t e r e t a i n e d on t h e b r o c c o l i l e a v e s and t h e l i g h t y e l l o w a r e a s t h a t i n d i c a t e l e a f i n j u r y . ( b ) The y e l l o w a r e a s e v e n t u a l l y become w h i t e n e c r o t i c a r e a s . ( B a r = 15 cm). -77--78-growth r a t e s a t 10 and 15 p e r c e n t N c o n c e n t r a t i o n s had i n c r e a s e d by t h e 2 8 t h d a y . Growth r a t e s o f v M a t r a ' ( c a u l i f l o w e r ) had a l s o i n c r e a s e d a f t e r an i n i t i a l d e c r e a s e f o r 15 and 20 p e r c e n t N c o n c e n t r a t i o n s ( F i g . 1 1 ) . Growth r a t e s had n e a r l y r e t u r n e d t o normal a f t e r one month. On t h e o t h e r h a n d , w h i l e x L u n e t ' ( B r u s s e l s s p r o u t s ) and ' E l g o n ' ( c a u l i f l o w e r ) showed t h e b e g i n n i n g s o f h i g h e r growth r a t e s f o r t h e 20 p e r c e n t N c o n c e n t r a t i o n , t h e r e was no s u c h t r e n d f o r t h e 10 and 15 p e r c e n t N c o n c e n t r a t i o n ( F i g . 1 1 ) . These d a t a s u g g e s t t h a t t h e l a t t e r two c u l t i v a r s a r e p a r t i c u l a r l y s e n s i t i v e t o ammonium n i t r a t e damage when t h e y a r e a t t h e 2 t o 3 t r u e l e a f s t a g e ( 1 9 8 7 ) . T h e r e a r e o t h e r r e p o r t s t h a t p l a n t g r o w t h r a t e s a r e i n i t i a l l y r e t a r d e d by ammonium n i t r a t e , b u t t h a t t h e p l a n t s r e c o v e r ( N a e g e r l y 1985, A g a m a l i a n 1 9 8 8 ) . In r e f e r e n c e t o b r o c c o l i , N a e g e r l y ( 1 9 8 5 ) m e n t i o n e d t h a t ammonium n i t r a t e c o u l d cause some c r o p damage, but t h e b r o c c o l i r e c o v e r e d w i t h i n a month o f t h e c h e m i c a l t r e a t m e n t . D e s p i t e t h e i n i t i a l d e c r e a s e i n t h e growth r a t e s o f some c u l t i v a r s by ammonium n i t r a t e , no s t a t i s t i c a l l y s i g n i f i c a n t (p<.05) e f f e c t on m a r k e t a b l e y i e l d o r y i e l d per p l a n t was found ( T a b l e 2 and 3; A ppendix 7 and 8 ) . T h i s s u g g e s t s t h a t even t h o s e c u l t i v a r s ('Lunet' ( B r u s s e l s s p r o u t s ) a n d x E l g o n ' ( c a u l i f l o w e r . ) ) w h o s e r a t e s o f d r y m a t t e r a c c u m u l a t i o n had shown no s i g n s o f i n c r e a s i n g a t 28 days a f t e r s p r a y i n g , had i n d e e d r e c o v e r e d by t h e t i m e t h e c r o p was h a r v e s t e d ( O c t o b e r f o r 'Lunet' ( B r u s s e l s s p r o u t s ) and September f o r ' E l g o n ' ( c a u l i f l o w e r ) ) . As s u c h t h e s e e x p e r i m e n t s d e m o n s t r a t e t h a t any i n i t i a l d e c r e a s e i n c r o p growth w i l l not n e c e s s a r i l y t r a n s l a t e i n t o d e c r e a s e d y i e l d s . -79-T a b l e 2. E f f e c t o f ammonium n i t r a t e on m a r k e t a b l e y i e l d s o f c o l e c r o p s and o n i o n . NH 4N0 3 c o n c e n t r a t i o n (% N) Crop C u l t i v a r 0 10 15 20 (1987) B r o c c o l i 'Emperor' 16.58* 16 .24 18. 12 14 .54 VSG1' 8.24 9 .72 10. 50 8 .04 C a u l i f l o w e r ' M a t r a ' 22.54 21 .32 21. 44 20 .80 ' E l g o n ' 20.40 22 .46 23. 20 25 .56 Cabbage ' E a r l y M a r v e l ' 21.14 21 .80 20. 46 21 .26 B r u s s e l s s p r o u t s 'Lunet' 35.98 37 .30 39. 04 41 .24 Onion 'White Lisbon'§ 1.02 1 .12 1. 22 0 .76 (1988) B r o c c o l i 'Emperor' 17.64 16 .44 18. 76 19 .26 'SGI'* 5.76 4. 64 5 .90 C a u l i f l o w e r ' M a tra' 30.48 23 .48 29. 00 23 .34 ' E l g o n ' 12.28 12 .52 16. 56 12 .08 Cabbage ' E a r l y M a r v e l ' 10.80 9 .44 14. 80 13 .18 B r u s s e l s s p r o u t s 'Lunet' 13.28 12 .42 13. 10 12 .46 Onion 'White L i s b o n ' 5 2.44 3 .82 2. 56 2 .54 f Average c r o p y i e l d ( t ha" ) o f 4 r e p l i c a t e s . F o r s t a t i s t i c a l a n a l y s i s o f d a t a see Appendix 7. § H a r v e s t e d as gr e e n b u n c h i n g o n i o n s . * O n l y t h r e e r e p l i c a t e s o f 0, 15, and 20 p e r c e n t N c o n c e n t r a t i o n s were used f o r 'SGI' i n 1988. -80-T a b l e 3. E f f e c t o f ammonium n i t r a t e on p e r p l a n t y i e l d o f c o l e c r o p s and o n i o n . NH NO c o n c e n t r a t i o n (% N) 4 3 Crop C u l t i v a r 0 10 15 20 (1987) B r o c c o l i 'Emperor' 663* 613 659 493 'SGI' 351 389 446 394 C a u l i f l o w e r ' M a t r a ' 1156 1093 1100 967 ' E l g o n ' 1046 1152 1190 1246 Cabbage ' E a r l y M a r v e l ' 813 808 910 880 B r u s s e l s s p r o u t s 'Lunet'* Onion 'White L i s b o n ' 5 14 13 12 10 (1988) B r o c c o l i 'Emperor' 0 705 609 736 740 ** 'SGI' 479 435 520 C a u l i f l o w e r ' M a t r a ' 1270 939 1160 1037 ' E l g o n ' 599 582 808 604 Cabbage ' E a r l y M a r v e l ' 415 402 519 439 B r u s s e l s s p r o u t s 'Lunet' 625 543 611 541 Onion 'White L i s b o n ' 5 12 10 13 13 f A v e r a g e y i e l d p e r p l a n t (g) o f 4 r e p l i c a t e s . F o r s t a t i s t i c a l a n a l y s i s o f d a t a see Appendix 8. § H a r v e s t e d as gr e e n b u n c h i n g o n i o n s . * Number o f 'Lunet' p l a n t s h a r v e s t e d was not r e c o r d e d i n 1987. ** O n l y t h r e e r e p l i c a t e s o f 0, 15, and 20 p e r c e n t N c o n c e n t r a t i o n s were used f o r 'SGI' i n 1988. -81-5. L e a f S u r f a c e U l t r a s t r u c t u r e and S u s c e p t i b i l i t y t o Ammonium N i t r a t e I n j u r y 5.1 I n t r o d u c t i o n To be e f f e c t i v e , a f o l i a r - a p p l i e d h e r b i c i d e must im p i n g e and be r e t a i n e d on t h e p l a n t s u r f a c e ( H o l l o w a y 1 9 7 0 ) . The m a i n p l a n t c h a r a c t e r i s t i c s a f f e c t i n g r e t e n t i o n a r e l e a f w e t t a b i l i t y , o r i e n t a t i o n , s i z e , and shape. L e a f w e t t a b i l i t y , w h i c h i s t h e most i m p o r t a n t f a c t o r ( H a i n e s e t a l . 1 9 8 5 , K i r k w o o d 1 9 8 7 ) , d e p e n d s on t h e c h e m i c a l and p h y s i c a l n a t u r e o f t h e e p i c u t i c u l a r wax ( E v a n s 1 9 8 2 ) and s u r f a c e r o u g h n e s s a r i s i n g f r o m c h a r a c t e r i s t i c s s u c h as v e n a t i o n , h a i r s , s e c r e t o r y g l a n d s , and e p i d e r m a l c e l l shape (Evans 1982, H o l l o w a y 1970, K i r k w o o d 1 9 8 7 ) . In g e n e r a l , wax i s abundant on l e a f s u r f a c e s t h a t r e s i s t w e t t i n g and i s s p a r s e o r a b s e n t on s u r f a c e s w h i c h a r e e a s i l y w e t t e d ( H o l l o w a y 1970). Ammonium n i t r a t e (800 L ha" 1; 20 p e r c e n t N as d e s c r i b e d p r e v i o u s l y on p. 43) s p r a y e d on a warm, sunny day b u r n s t h e f o l i a g e o f s e v e r a l b r o a d l e a f weeds ( e . g . s h e p h e r d ' s - p u r s e , cudweed, r e d r o o t p i g w e e d , and 1ady's-thumb) w i t h o u t s i g n i f i c a n t damage t o c o l e ( b r o c c o l i , B r u s s e l s s p r o u t s , cabbage, c a u l i f l o w e r ) and o n i o n c r o p s ( C h a p t e r 4; B i t t e r l i c h and U p a d h y a y a 1 9 8 8 ) . Some weeds, such as l a m b ' s - q u a r t e r s and a n n u a l b l u e g r a s s , a l s o t o l e r a t e t h i s t r e a t m e n t . The o b j e c t i v e o f t h i s s t u d y was t o d e t e r m i n e i f t o l e r a n c e t o ammonium n i t r a t e i s due t o t h e p r e s e n c e o f an e p i c u t i c u l a r wax l a y e r w h i c h h e l p s r e p e l t h e s a l t s o l u t i o n . -82-5.2 M a t e r i a l s and Methods S e e d l i n g s o f b r o c c o l i (Brassica oleracea v a r . botrytis, c v . E m p e r o r ) , c a b b a g e ( f l . oleracea v a r . capitata c v . E a r l y M a r v e l ) , c a u l i f l o w e r ( f l . oleracea v a r . botrytis, c v . M a t r a ) , o n i o n (Allium cepa c v . W h i t e L i s b o n ) , r e d r o o t p i g w e e d (Amaranthus retroflexus), s h e p h e r d ' s - p u r s e (Capsella bursa-pastoris), l a d y ' s - t h u m b (Polygonum persicaria), common g r o u n d s e l (Senecio vulgaris), l a m b ' s - q u a r t e r s (Chenopodium album), and annual b l u e g r a s s (Poa annua) were used i n t h i s s t u d y . B r o c c o l i and cabbage s e e d s were s u p p l i e d by S t o k e s L t d . ( S t . C a t h a r i n e s , O n t . ) , c a u l i f l o w e r by Royal S l u i s ( E n k h u i z e n , N e t h e r l a n d s ) , and o n i o n by B u c k e r f i e l d s L t d . ( A b b o t s f o r d , B . C . ) . Weed s e e d s were c o l l e c t e d from n a t u r a l p o p u l a t i o n s i n B r i t i s h C o l u m b i a . Seeds were sown i n 11.5 cm p l a s t i c p o t s -and s e e d l i n g s were grown i n g r o w t h chambers (22°C, 16 h p h o t o p e r i o d and c a . 210 jjmol m" 2s - 1 l i g h t i n t e n s i t y ) . The a d a x i a l l e a f s u r f a c e o f s e e d l i n g s a t t h e o n e - t o - f o u r t r u e l e a f s t a g e was examined by s c a n n i n g e l e c t r o n m i c r o s c o p e (SEM). The a b a x i a l s u r f a c e was not s t u d i e d because t h e ammonium n i t r a t e s p r a y f a l l s p r i m a r i l y on t h e a d a x i a l s u r f a c e . Fresh, uncoated leaf samples. S m a l l s q u a r e s ( a p p r o x i m a t e l y 4 mm2) o f l e a f t i s s u e were c u t w i t h a r a z o r b l a d e and mounted ( a d a x i a l s i d e f a c i n g up) on a l u m i n i u m s t u d s u s i n g a d h e s i v e t a b s . L e a f s u r f a c e u l t r a s t r u c t u r e was e x a m i n e d i m m e d i a t e l y u s i n g a C a m b r i d g e 250T SEM (10 k V ) . -83-Fresh, coated leaf samples. L e a f samples were c u t and mounted as d e s c r i b e d a b o v e . The s p e c i m e n s w e r e g o l d c o a t e d ( c a . 2 0 0 - 3 0 0 A t h i c k n e s s ) u s i n g a N a n o t e c h Semprep s p u t t e r i n g d e v i c e and v i e w e d i m m e d i a t e l y by SEM (20 k V ) . Cellulose acetate film stripping of epicuticular wax. A c e l l u l o s e a c e t a t e (Sigma, U.S.A.) s o l u t i o n ( 5 % w/v i n a c e t o n e ) was a p p l i e d t h i c k l y t o t h e a d a x i a l l e a f s u r f a c e w i t h a s m a l l p a i n t b r u s h ( B a k e r e t a l . 1983, S i l c o x a nd H o l l o w a y 1 9 8 6 ) . The f i l m was a l l o w e d t o d r y a t r o o m t e m p e r a t u r e and g e n t l y p e e l e d t o remove t h e s u r f a c e wax. S t r i p p e d l e a v e s were g o l d - c o a t e d and examined by SEM (20 k V ) . R e s u l t s and D i s c u s s i o n The l e a f s u r f a c e ( a d a x i a l ) o f ammonium n i t r a t e - s u s c e p t i b l e s p e c i e s (common g r o u n d s e l , l a d y ' s - t h u m b , r e d r o o t pigweed, and shepherd's p u r s e ) g r o w n u n d e r t h e same c o n d i t i o n s h a d l i t t l e o r no c r y s t a l l i n e e p i c u t i c u l a r wax ( F i g . 1 6 a - e ) . The l e a f s u r f a c e o f s h e p h e r d ' s - p u r s e had two t y p e s o f t r i c h o m e s : (1) a s t e l l a t e t r i c h o m e t h a t l i e s f l a t on t h e l e a f s u r f a c e and (2) a l o n g , u p r i g h t , c y l i n d r i c a l , and p o i n t e d t r i c h o m e ( F i g . 1 6 h ) . S i m i l a r l y , l o n g unbranched t r i c h o m e s , w h i c h o f t e n c o l l a p s e d under t h e SEM vacuum, were p r e s e n t on t h e l e a f s u r f a c e s o f lady's-thumb and common g r o u n d s e l ( F i g . 1 6 f , g ) . I n t e r e s t i n g l y , t h e r e appeared t o be a gap where t h e s t e l l a t e t r i c h o m e o f s h e p h e r d ' s - p u r s e was c o n n e c t e d t o t h e c u t i c l e ( F i g . 1 6 i , j ) . Removal o f t h e s e s t e l l a t e t r i c h o m e s by c e l l u l o s e a c e t a t e s t r i p p i n g r e v e a l e d u n i f o r m , c i r c u l a r h o l e s on t h e l e a f s u r f a c e ( F i g . 1 6 k ) . -84-F i g . 16. L e a f s u r f a c e ( a d a x i a l ) m o r p h o l o g y o f s u s c e p t i b l e weed s p e c i e s : ( a ) 1 s t t r u e - l e a f o f s h e p h e r d ' s - p u r s e ( u n c o a t e d , b a r = 10 urn), (b) 2nd t r u e - l e a f o f c h i c k w e e d ( g o l d c o a t e d , b a r = 10 um), ( c ) 2nd t r u e - l e a f o f l a d y ' s - t h u m b ( g o l d c o a t e d , b a r = 10 /jm), (d) 2nd t r u e - l e a f o f r e d r o o t pigweed ( g o l d c o a t e d , b a r = 4 /jm), and (e) 4 t h t r u e - l e a f o f common g r o u n d s e l ( g o l d c o a t e d , b a r = 10 IM). T r i c h o m e s on ( f ) 2nd t r u e - l e a f o f lady's-thumb ( g o l d c o a t e d , b a r = 100 /xm), (g) 2nd t r u e - l e a f o f g r o u n d s e l ( u n c o a t e d , b a r = 100 /an), and (h) s t i l l e x p a n d i n g 4 t h t r u e - l e a f o f s h e p h e r d ' s - p u r s e ( u n c o a t e d , b a r = 200 /an). Note: t r i c h o m e s c o l l a p s e d t o v a r y i n g d e g r e e s under SEM vacuum, ( i ) S t e l l a t e t r i c h o m e on t h e 1 s t t r u e - l e a f o f s h e p h e r d ' s - p u r s e ( u n c o a t e d , b a r = 40 /an) showing t h e gap below ( a r r o w ) , (j) an e n l a r g e m e n t (3.1x) o f t h e gap ( a r r o w ) shown i n ( i ) , and (k) h o l e s ( a r r o w s ) l e f t a f t e r s t r i p p i n g o f t h e s t e l l a t e t r i c h o m e s ( u n c o a t e d , b a r = 100 /im). -85-F i g . 16 -86-L e a v e s o f t o l e r a n t c r o p ( b r o c c o l i , c a b b a g e , c a u l i f l o w e r , and o n i o n s ) and weed (annual b l u e g r a s s and l a m b ' s - q u a r t e r s ) s p e c i e s r e v e a l e d a h e a vy c r y s t a l l i n e e p i c u t i c u l a r wax l a y e r on t h e i r a d a x i a l s u r f a c e ( F i g . 1 7 a - e ) . The wax d e p o s i t i o n o c c u r r e d i n t h e f o r m o f t u b u l e s , d e n d r i t e s ( o f t e n i n t e r l o c k i n g ) and/or p l a t e l e t s ( s e e B a k e r 1982 f o r a d e s c r i p t i o n o f t h e s e s t r u c t u r e s ) . L a m b ' s - q u a r t e r s a l s o had d i s t i n c t b a l l o o n - l i k e t r i c h o m e s i n a d d i t i o n t o t h i n , u p r i g h t wax p l a t e l e t s ( F i g . 1 7 e , f and r e f e r e n c e H a r t 1 9 7 9 ) . No o t h e r d i s t i n c t s u r f a c e s t r u c t u r e s were seen on t h e a d a x i a l s u r f a c e o f o t h e r t o l e r a n t s p e c i e s . Removal o f e p i c u t i c u l a r wax from cabbage l e a v e s ( t w o - t o - t h r e e l e a f s t a g e ) by c e l l u l o s e a c e t a t e s t r i p p i n g method ( F i g . 18a) i n c r e a s e d s o l u t i o n r e t e n t i o n ( F i g . 18b) and s a l t i n j u r y ( F i g . 1 8 c ) . However, t h e s o l u t i o n d i d not wet t h e s t r i p p e d l e a f s u r f a c e e v e n l y and l e a f - k i l l was n o t c o m p l e t e . C o t y l e d o n s o f c o l e c r o p s , w h i c h have v e r y l i t t l e o r no e p i c u t i c u l a r wax ( C a p o r n and H u t c h i n s o n 1 9 8 6 ) , r e t a i n e d t h e ammonium n i t r a t e s o l u t i o n ( F i g . 18b) and d i e d . The p r e s e n c e o f c r y s t a l l i n e e p i c u t i c u l a r wax p r o t e c t s l e a f s u r f a c e s f r o m f o l i a r a p p l i e d c h e m i c a l s by d e c r e a s i n g t h e i r r e t e n t i o n ( J u n i p e r 1959). E p i c u t i c u l a r wax a f f e c t s t h e c o n t a c t a n g l e o f t h e s p r a y d r o p l e t s (Evans 1982) wh i c h p r e v e n t s l e a f w e t t i n g ; t h e d r o p l e t s bead and r o l l o f f t h e p l a n t . Our r e s u l t s i n d i c a t e t h a t e p i c u t i c u l a r wax on t h e a d a x i a l l e a f s u r f a c e p r o t e c t s t o l e r a n t s p e c i e s f r o m ammonium n i t r a t e i n j u r y by r e p e l l i n g t h e s a l t s o l u t i o n . The s u s c e p t i b l e s p e c i e s a r e k i l l e d because t h e y have l i t t l e o r no e p i c u t i c u l a r wax and, t h e r e f o r e , a r e n o t a b l e t o r e p e l t h e s o l u t i o n . The i n c r e a s e i n s o l u t i o n r e t e n t i o n and f o l i a r i n j u r y i n cabbage f o l l o w i n g c r y s t a l l i n e e p i c u t i c u l a r wax -87-F i g . 17. C r y s t a l l i n e e p i c u t i c u l a r wax d e p o s i t i o n on t h e a d a x i a l l e a f s u r f a c e o f t o l e r a n t s p e c i e s ( g o l d c o a t e d s a m p l e s ) : (a) 2nd t r u e - l e a f o f b r o c c o l i ( b a r = 4 /im), (b) 2nd t r u e - l e a f o f c a u l i f l o w e r ( b a r = 4 /im), ( c ) 1 s t t r u e - l e a f o f o n i o n ( b a r = 4 /im), (d) 2nd t r u e - l e a f o f annual b l u e g r a s s ( b a r = 2 /im), and (e) 1 s t t r u e - l e a f o f l a m b ' s - q u a r t e r s ( b a r = 10 /im). ( f ) B a l l o o n - l i k e s t r u c t u r e s on t h e 1 s t t r u e - l e a f o f l a m b ' s - q u a r t e r s ( u n c o a t e d , b a r = 100 /im). -88-F i g . 17 -89-F i g . 18. (a) S u r f a c e o f t h e 1 s t t r u e - l e a f o f cabbage w i t h ( l e f t ) and w i t h o u t ( r i g h t ) c r y s t a l l i n e e p i c u t i c u l a r wax ( g o l d c o a t e d ; b a r = 20 nm). C r y s t a l l i n e wax was r e m o v e d u s i n g t h e c e l l u l o s e a c e t a t e f i l m s t r i p p i n g method d e s c r i b e d i n t h e t e x t . S i m i l a r r e s u l t s w e r e o b t a i n e d w i t h b r o c c o l i and c a u l i f l o w e r , ( b ) C o m p a r i s o n o f s o l u t i o n r e t e n t i o n by s t r i p p e d and u n s t r i p p e d l e a v e s o f cabbage i m m e d i a t e l y a f t e r ammonium n i t r a t e a p p l i c a t i o n . Note t h e i n c r e a s e d r e t e n t i o n by t h e s t r i p p e d ( l o w e r r i g h t ) v e r s u s t h e u n s t r i p p e d ( u p p e r l e f t and m i d d l e ) l e a v e s and t h e degr e e o f s p r a y r e t e n t i o n by c o t y l e d o n s ( a r r o w ) , ( c ) C o m p a r i s o n o f f o l i a r i n j u r y i n u n s t r i p p e d ( l e f t ) and s t r i p p e d ( r i g h t ) cabbage p l a n t s 4 days a f t e r s p r a y i n g w i t h ammonium n i t r a t e s o l u t i o n . -91-removal s u p p o r t s t h i s c o n c l u s i o n . The f a c t t h a t t h e s a l t s o l u t i o n d i d n o t wet t h e s t r i p p e d l e a f s u r f a c e e v e n l y and t h a t l e a f - k i l l was n o t c o m p l e t e s u g g e s t s t h a t amorphous c u t i c u l a r wax o f f e r s some p r o t e c t i o n t o t h e s e l e a v e s . E p i c u t i c u l a r wax not o n l y d e c r e a s e s s o l u t i o n r e t e n t i o n , but may a l s o p r e v e n t t h e s a l t s o l u t i o n and s a l t c r y s t a l s from coming i n c o n t a c t w i t h t h e l e a f t i s s u e . L e a f a n g l e and t r i c h o m e s can a l s o i n f l u e n c e s o l u t i o n r e t e n t i o n and a b s o r p t i o n . The s t e e p e r t h e a n g l e a t w h i c h a drop s t r i k e s a l e a f , t h e more l i k e l y t h e drop w i l l r o l l o f f . T h e r e f o r e , u p r i g h t l e a v e s l i k e t h o s e o f o n i o n o r annual b l u e g r a s s c o n t r i b u t e t o ammonium n i t r a t e t o l e r a n c e . A c c o r d i n g l y , h o r i z o n t a l l e a v e s s u c h as t h o s e o f s h e p h e r d ' s - p u r s e and r e d r o o t p i g w e e d w i l l i n c r e a s e s o l u t i o n r e t e n t i o n and p o t e n t i a l l e a f i n j u r y . In a d d i t i o n , t h e p r e s e n c e o f t r i c h o m e s on t h e l e a f s u r f a c e o f some s u s c e p t i b l e s p e c i e s may a l s o i n c r e a s e ammonium n i t r a t e r e t e n t i o n ( C h a l l e n 1962). In s h e p h e r d ' s - p u r s e , t h e gap p r e s e n t where t h e s t e l l a t e t r i c h o m e s j o i n t h e c u t i c l e may o f f e r a p r e f e r e n t i a l s i t e f o r ammonium n i t r a t e i n j u r y . T h i s gap may a l s o e x p l a i n t h e h i g h e r a b s o r p t i o n o f h e r b i c i d e s r e p o r t e d a t t h e base o f t r i c h o m e s i n o t h e r s p e c i e s ( K i r k w o o d 1987). Many s o i l , c l i m a t i c , and p l a n t f a c t o r s a r e known t o i n f l u e n c e e p i c u t i c u l a r wax d e p o s i t i o n on l e a f s u r f a c e s . These i n c l u d e m o i s t u r e s t r e s s ( B a k e r and P r o c o p i o u 1980, Bengston e t a l . 1978, Hunt and Baker 1982, Saneoka and Ogata 1987), t h e impact o f r a i n d r o p s w h i c h p h y s i c a l l y removes e p i c u t i c u l a r wax ( B a k e r and Hunt 1986), t e m p e r a t u r e ( A r m s t r o n g and W h i t e c r o s s 1976, Baker 1974), l i g h t i n t e n s i t y ( B a k e r 1974), r e l a t i v e -92-h u m i d i t y ( B a k e r 1974, Hunt and Baker 1982), a i r p o l l u t a n t s ( K o z i o l and C o w l i n g 1 9 8 1 ) , and l e a f age ( B a k e r and Hunt 1981). How t h e s e f a c t o r s i n f l u e n c e s u s c e p t i b i l i t y t o f e r t i l i z e r b u r n i n g r e m a i n s t o be d e t e r m i n e d . N e v e r t h e l e s s , t h e f a c t t h a t c r y s t a l l i n e wax d e p o s i t i o n d i f f e r s i n t o l e r a n t a n d s u s c e p t i b l e s p e c i e s i s s i g n i f i c a n t . M e a s u r e m e n t o f e p i c u t i c u l a r wax d e p o s i t i o n c o u l d a l l o w a g r o n o m i s t s and p l a n t b r e e d e r s t o s c r e e n s p e c i e s and g e n e t i c m a t e r i a l f o r t o l e r a n c e t o f e r t i l i z e r b u r n i n g w i t h o u t e x t e n s i v e f i e l d t r i a l s . Indeed, f e r t i l i z e r b u r n i n g i s an a t t r a c t i v e weed c o n t r o l o p t i o n because: 1) i t i s e n v i r o n m e n t a l l y s a f e compared t o many o t h e r s y n t h e t i c o r g a n i c h e r b i c i d e s i f a p p l i e d a t o r below t h e c u r r e n t l y recommended f e r t i l i z e r r a t e s , (2) i t poses a minimum h e a l t h h a z a r d t o t h e a p p l i c a t o r , ( 3 ) b e c a u s e ammonium n i t r a t e i s a f e r t i l i z e r , p e s t i c i d e r e g i s t r a t i o n , a pro b l e m i n mi n o r c r o p s , may n o t be as d i f f i c u l t t o o b t a i n , and (4) t h e c h e m i c a l a l s o f e r t i l i z e s t h e c r o p i f t h e c r o p i s i r r i g a t e d t h r e e - t o - f o u r d a y s a f t e r ammonium n i t r a t e a p p l i c a t i o n . I n t h e F r a s e r V a l l e y ( B . C . ) , b r o c c o l i y i e l d has been r e p o r t e d t o i n c r e a s e w i t h i n c r e a s e d a p p l i c a t i o n s o f N up t o 250 kg ha" 1 ( K o w a l e n k o and H a l l 1 9 8 7 ) . A r a t e o f 250 kg ha" 1 i s s i m i l a r t o t h e r a t e s used i n t h i s s t u d y ( C h a p t e r 4; 224, 229, 249, and 257 kg h a " 1 ) . -93-6. C o n c l u s i o n L a m b ' s - q u a r t e r s (Chenopodium album) i s a v e r y c o m p e t i t i v e weed s p e c i e s when grown w i t h d i r e c t seeded b r o c c o l i . Low d e n s i t i e s o f t h e weed can a f f e c t b r o c c o l i g r o w t h a t o n l y 28 t o 36 days a f t e r s e e d i n g . Y i e l d d a t a f i t t e d t o a r e c t a n g u l a r h y p e r b o l i c model i n d i c a t e s t h a t one l a m b ' s - q u a r t e r s p l a n t m~2 c a n r e d u c e t o t a l c r o p y i e l d by 18 t o 20 p e r c e n t and m a r k e t a b l e y i e l d (heads >10 cm a c r o s s ) by 22 t o 37 p e r c e n t . L a m b ' s - q u a r t e r s r e d u c e d t o t a l y i e l d by r e d u c i n g a v e r a g e head w e i g h t and not by l o w e r i n g t h e number o f heads p e r p l o t . On t h e o t h e r hand, t h e weed r e d u c e d m a r k e t a b l e y i e l d by r e d u c i n g both t h e a v e r a g e head w e i g h t and t h e number o f heads p e r p l o t . The s t r o n g c o m p e t i t i v e a b i l i t y o f t h e weed i n d i c a t e s t h a t e a r l y c o n t r o l o f l a m b ' s - q u a r t e r s i s e s s e n t i a l i f weed l o s s e s a r e t o be a v o i d e d . F o r t u n a t e l y t h i s weed can be c o n t r o l l e d by t r i f l u r a l i n o r DCPA. T e s t i n g o f l i q u i d ammonium n i t r a t e f o r weed c o n t r o l i n c o l e c r o p s i n d i c a t e s t h a t s h e p h e r d ' s - p u r s e (Capsella bursa-pastoris), c h i c k w e e d {Stellaria media), cudweed {Gnaphalium uliginosum), and r e d r o o t pigweed {Amaranthus retroflexus) a r e c o n t r o l l e d , but l a m b ' s - q u a r t e r s , p u r s l a n e (Portulaca oleracea), and annual b l u e g r a s s {Poa annua) a r e n o t . Corn s p u r r y (Spergula arvensis) i s b u r n t back b u t n o t a l w a y s c o n t r o l l e d . Ammonium n i t r a t e c a n n o t p r e v e n t a m i x e d weed p o p u l a t i o n f r o m c a u s i n g c r o p f a i l u r e when (1) t h e i n i t i a l weed d e n s i t y i s v e r y l a r g e , (2) t h e r e a r e many r e s i s t a n t weeds p r e s e n t , and (3) many o f t h e s u s c e p t i b l e weeds r e c o v e r from t h e ammonium n i t r a t e b u r n i n g . However, a weed p o p u l a t i o n o f o n l y s u s c e p t i b l e s h e p h e r d ' s - p u r s e i s a d e q u a t e l y c o n t r o l l e d w i t h no -94-l o s s i n b r o c c o l i y i e l d even when t h e i n i t i a l weed p o p u l a t i o n i s as h i g h as 988 p l a n t s n f 2 . C r o p c u l t i v a r s v a r i e d i n t h e damage t h e y i n c u r r e d f r o m t h e ammonium n i t r a t e s p r a y . The two c a u l i f l o w e r c u l t i v a r s , ' M a t r a ' and ' E l g o n ' a p p e a r t o be t h e most v u l n e r a b l e . C o mpared t o t h e o t h e r c u l t i v a r s , t h e r a t e o f c a u l i f l o w e r g r o w t h was most r e t a r d e d . 'SGI' ( b r o c c o l i ) and 'Lunet' ( B r u s s e l s s p r o u t s ) appear t o be s u s c e p t i b l e when y o u n g . A l t h o u g h g r o w t h r a t e s o f t h e s e c u l t i v a r s may i n i t i a l l y be r e t a r d e d , t h e y r e c o v e r and y i e l d as w e l l as c o n t r o l s . ' E m p e r o r ' ( b r o c c o l i ) , ' E a r l y M a r v e l ' ( c a b b a g e ) , and 'White L i s b o n ' ( o n i o n ) appear t o be t o l e r a n t t o t h e ammonium n i t r a t e s p r a y . The l e a f s u r f a c e o f t o l e r a n t c r o p and weed s p e c i e s was p r o t e c t e d by an e p i c u t i c u l a r c r y s t a l l i n e wax l a y e r i n t h e f o r m o f d e n d r i t e s , t u b u l e s , and p l a t e l e t s which causes t h e f e r t i l i z e r t o bead up and r o l l o f f t h e l e a v e s . The wax l a y e r may a l s o p r e v e n t t h e ammonium n i t r a t e r e t a i n e d f r o m coming i n c o n t a c t w i t h t h e p l a n t c u t i c l e . S u s c e p t i b l e s p e c i e s have no c r y s t a l l i n e wax and r e l a t i v e l y smooth s u r f a c e s a n d , h e n c e , t h e y r e t a i n t h e ammonium n i t r a t e w h i c h c a u s e s l e a f d e a t h o r s e v e r e i n j u r y . Because e p i c u t i c u l a r wax i s t h e b a s i s o f c r o p t o l e r a n c e c a r e must be t a k e n not t o s p r a y u n l e s s t h e wax l a y e r has d e v e l o p e d s u f f i c i e n t l y . E n v i r o n m e n t a l c o n d i t i o n s and p l a n t age a r e known t o a f f e c t wax m o r p h o l o g y and amount. T h e r e f o r e , f u r t h e r s t u d y i s r e q u i r e d t o e l u c i d a t e optimum s p r a y i n g t i m e s . N o t w i t h s t a n d i n g some o f t h e problems a s s o c i a t e d w i t h c r o p t o l e r a n c e , ammonium n i t r a t e h o l d s t h e p r o m i s e o f b e i n g a p o t e n t i a l l y v a l u a b l e weed c o n t r o l o p t i o n f o r c o l e c r o p g r o w e r s . -95-7. B i b l i o g r a p h y A g a m a l i a n , H.S. 1976. The e f f e c t o f weed p o p u l a t i o n and t h e i r c o n t r o l on b r o c c o l i y i e l d s . Weed S c i . Soc. Amer. A b s t r . 58:26. A g a m a l i a n , H.S. 1983. C o m p e t i t i o n o f annual weeds i n b r o c c o l i . P r o c . Western Soc. Weed S c i . 36:192. A g a m a l i a n , H.S. 1984. Post-emergent weed c o n t r o l i n c r u c i f e r s w i t h n i t r o g e n o u s f e r t i l i z e r s . P r o c . West. Soc. Weed S c i . 37:57-59. A g a m a l i a n , H.S. 1988. Weed c o n t r o l i n c r u c i f e r c r o p s w i t h n i t r o g e n f e r t i l i z e r s . C a l i f . A g r i c . 6:16-17. A l d r i c h , R . J . 1987. P r e d i c t i n g c r o p y i e l d r e d u c t i o n s from weeds. Weed T e c h n o l . 1:199-206. A r m s t r o n g , D.J., W h i t e c r o s s , M.I. 1976. Temperature e f f e c t s on f o r m a t i o n and f i n e s t r u c t u r e o f Brassica napus l e a f waxes. A u s t . J . B o t . 24:309-318. A v a t o , P., B i a n c h i , G., Nay ale, A., S a l a m i n i , F., G e n t i n e t t a , E. 1987. E p i c u t i c u l a r waxes o f maize as a f f e c t e d by t h e i n t e r a c t i o n o f mutant g78 w i t h g73, g74, and g715. L i p i d s 22:11-16. B a k e r , E.A. 1974. The i n f l u e n c e o f e n v i r o n m e n t on l e a f wax development i n Brassica oleracea v a r . gemmifera. New P h y t o l . 73:955-966. B a k e r , E.A., Hunt, G.M. 1981. Developmental changes i n l e a f e p i c u t i c u l a r waxes i n r e l a t i o n t o f o l i a r p e n e t r a t i o n . New P h y t o l . 88:731-747. B a k e r , E.A., Hunt, G.M. 1986. E r o s i o n o f waxes from l e a f s u r f a c e s by s i m u l a t e d r a i n . New P h y t o l . 102:161-173. B a k e r , E.A., Hunt, G.M., S t e v e n s , P.J.G. 1983. S t u d i e s o f p l a n t c u t i c l e and s p r a y d r o p l e t i n t e r a c t i o n s : a f r e s h a p p r o a c h . P e s t i c . S c i . 14:645-658. B a k e r , E.A., P r o c o p i o u , J . 1980. E f f e c t o f s o i l m o i s t u r e s t a t u s on l e a f s u r f a c e wax y i e l d o f some d r o u g h t - r e s i s t a n t s p e c i e s . J . H o r t i c . S c i . 55:85-87. B e n g s t o n , C , L a r s s o n , S., L i l j e n b e r g , C. 1978. E f f e c t s o f w a t e r s t r e s s on c u t i c u l a r t r a n s p i r a t i o n r a t e and amount and c o m p o s i t i o n o f e p i c u t i c u l a r wax i n s e e d l i n g s o f s i x o a t v a r i e t i e s . P h y s i o l . P l a n t . 44:319-324. B e v e r l y , R.B., J a r r e l l , W.M., L e t e y , J . J r . 1986. A n i t r o g e n and w a t e r r e s p o n s e s u r f a c e f o r s p r i n k l e r - i r r i g a t e d b r o c c o l i . A g r o n. J . 78:91-94. -96-B i t t e r l i c h , I . , Upadhyaya, M.K. 1988. Postemergence weed, c o n t r o l i n c o l e c r o p s and o n i o n u s i n g ammonium n i t r a t e s o l u t i o n . Weed S c i . Soc. Amer. A b s t r . 28:93. 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L i p i d w a t e r b a r r i e r s i n b i o l o g i c a l s y s t e m s . P r o g . L i p i d Res. 28:1-33. H a i n e s , B.L., J e r n s t e d t , J.A., N e u f e l d , H.S. 1985. D i r e c t f o l i a r e f f e c t s o f s i m u l a t e d a c i d r a i n . I I . L e a f s u r f a c e c h a r a c t e r i s t i c s . New P h y t o l . 99:407-416. H a l l , D.M., J o n e s , R.L. 1961. P h y s i o l o g i c a l s i g n i f i c a n c e o f s u r f a c e wax on l e a v e s . N a t u r e (Lond.) 191:95-96. H a r t , C A . 1979. Use o f t h e s c a n n i n g e l e c t r o n m i c r o s c o p e and c a t h o d o l u m i n e s c e n c e i n s t u d y i n g t h e a p p l i c a t i o n o f p e s t i c i d e s t o p l a n t s . P e s t i c . S c i . 10:341-357. -98-Hartley, G.S., Burnskill, R.T. 1958. R e f l e c t i o n o f w a t e r d r o p s f r o m s u r f a c e s . In S u r f a c e phenomena i n c h e m i s t r y and b i o l o g y . Edited by J . F . D a n i e l 1 i, K.G.A. 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Path a n a l y s i s o f growth d i f f e r e n c e s between weed and nonweed p o p u l a t i o n s o f p o o r j o e (Diodia feres) i n c o m p e t i t i o n w i t h soybean (Glycine max). Weed S c i . 37:129-136. Juniper, B.E. 1959. The s u r f a c e s o f p l a n t s . Endeavour 18: 20-25. Juniper, B.E., Jeffree, C.E. 1983. P l a n t s u r f a c e s . Edward A r n o l d ( P u b l i s h e r s ) L t d . , London, p.8. Keddy, P.A., Shipley, B. 1989. C o m p e t i t i v e h i e r a r c h i e s i n herbaceous p l a n t c o m m u n i t i e s . O i k o s 54:234-241. -99-Kirkwood, R.C. 1987. Uptake and movement o f h e r b i c i d e s from p l a n t s u r f a c e s and t h e e f f e c t s o f f o r m u l a t i o n and e n v i r o n m e n t upon them. In P e s t i c i d e s on p l a n t s u r f a c e s . Edited by H.J. C o t t r e l l . John W i l e y and Sons, S a l i s b u r y and W i l t s h i r e , pp. 1-25. Kowalenko, C.G., Hall, J.W. 1987. 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Canopy development, l e a f demography and growth dynamics o f wheat and t h r e e weed s p e c i e s g r o w i n g i n pure and mixed s t a n d s . J . A p p l . E c o l . 23:929-944. Martin, J.T. , Juniper, B.E. 1970. The c u t i c l e s o f p l a n t s . Edward A r n o l d ( P u b l i s h e r s ) L t d . pp.223-234. Mayeux, H.S. Jr . , Jordan, W.R., Meyer, R.E., Meola, S.M. 1981. E p i c u t i c u l a r wax on goldenweed (Isocoma spp.) l e a v e s : v a r i a t i o n w i t h s p e c i e s and s e a s o n . Weed S c i . 29:389-393. Naegerly, S.K. 1985. Weed and f e e d - a S a l i n a s v a l l e y t e c h n i q u e . Am. Veg. Grow. 33(4):24-25. Nelson, D.C, Nylund, R.E. 1962. C o m p e t i t i o n between peas grown f o r p r o c e s s i n g and weeds. Weeds 10:224-229. Nieuwhof, M. 1969. C o l e c r o p s : b o t a n y , c u l t i v a t i o n , and u t i l i z a t i o n . U n i v e r s i t y P r e s s Aberdeen, London, p.27. Patterson, D.T. 1985. 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The use o f ammonium n i t r a t e f o r weed c o n t r o l i n c o l e c r o p s . [ P r e p a r e d f o r ] B.C. growers s h o r t c o u r s e , [ A b b o t s f o r d , B.C.] F e b r u a r y 5, 1986. Oregon S t a t e U n i v e r s i t y , E x t e n s i o n S e r v i c e . [ C o r v a l l i s , OR] pp. 1-5. Roberts, H.A., Bond, W. 1975. Combined t r e a t m e n t s o f p r o p a c h l o r and t r i f l u r a l i n f o r weed c o n t r o l i n cabbage. Weed Res., 15:195-198. Roberts, H.A., Bond, W., Hewson, R.T. 1976. Weed c o m p e t i t i o n i n d r i l l e d cabbage. Ann. A p p l . B i o l . 84:91-95. Saneoka, H., Ogata, S. 1987. R e l a t i o n s h i p between w a t e r use e f f i c i e n c y and c u t i c u l a r wax d e p o s i t i o n i n warm season f o r a g e c r o p s grown under w a t e r d e f i c i t c o n d i t i o n s . S o i l S c i . P l a n t N u t r . 33:439-448. Schweizer, E.E. 1983. 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E n v i r o n m e n t a l e f f e c t s on e p i c u t i c u l a r waxes o f Brassica napus. A u s t . J . B o t . 20:87-95. Wolter, M., Barthlott, W., Knoche, N., Noga, G.J. 1988. C o n c e n t r a t i o n e f f e c t s and r e g e n e r a t i o n o f e p i c u t i c u l a r waxes a f t e r t r e a t m e n t w i t h T r i t o n X-100 s u r f a c t a n t . Angew. B o t . 62:53-62. -102-A p p e n d i x 1. R e l a t i v e s u s c e p t i b i l i t y o f weed s p e c i e s i n 1987. R e g r e s s i o n a n a l y s i s o f weed numbers b e f o r e and a f t e r ammonium n i t r a t e a p p l i c a t i o n . Weed Days* * a ** m R 2 *** P Shepherd's-purse -3 98.26 -0.12 0.00 0.899 +2 95.40 -3.05 0.43 0.000 +46§ 96.36 -3.08 0.40 0.000 Chi ckweed -3 80.29 -1.46 0.09 0.063 +2 74.65 -2.73 0.42 0.000 +46 54.51 -1.65 0.37 0.000 Annual Bluegrass -3 9.63 0.14 0.01 0.490 +2 9.62 0.17 0.02 0.456 +46 11.06 0.59 0.06 0.124 Corn Spurry -3 28.82 0.67 0.01 0.486 +2 23.74 0.35 0.01 0.582 +46 26.66 -0.39 0.01 0.512 Cudweed -3 415.23 10.00 0.02 0.361 +2 420.97 -18.28 0.21 0.003 +46 291.51 -11.43 0.16 0.010 Lamb's-quarters -3 38.18 -0.05 0.00 0.943 +2 39.78 -0.20 . 0.00 0.758 Purslane -3 74.57 -0.84 0.01 0.667 +2 62.80 -0.29 0.00 0.873 +46 82.66 -1.16 0.01 0.599 Redroot Pigweed -3 47.68 -1.66 0.05 0.193 +2 36.20 -2.11 0.20 0.004 +46 48.58 -2.50 0.14 0.018 Total -3 798.54 6.84 0.01 0.599 +2 769.54 -25.76 0.23 0.001 +46 637.44 -19.80 0.21 0.003 F o o t n o t e s on n e x t page. -103-Weed d e n s i t i e s ( p l a n t s n f 2 ) b e f o r e ammonium n i t r a t e a p p l i c a t i o n were f i t t e d t o t h e model d ^ b j + b ^ ( E q u a t i o n 3 d e s c r i b e d on p . 4 4 ) . Weed d e n s i t i e s ( p l a n t s n f 2 ) a f t e r ammonium n i t r a t e a p p l i c a t i o n were f i t t e d t o t h e model d a=a 1+a 2c a ( E q u a t i o n 4 d e s c i b e d on p.4 5 ) . There were e i g h t r e p l i c a t e s p e r ammonium n i t r a t e t r e a t m e n t ( 0 , 7.5, 10, 15 and 20 p e r c e n t N). t Days b e f o r e (-) and a f t e r (+) ammonium n i t r a t e a p p l i c a t i o n . * a = dependent v a r i a b l e i n t e r c e p t ( b j o r a ^ f o r e i t h e r d / 3=b 1+b 2c^ ( d e s c r i b e s weed d e n s i t y a t 3 days b e f o r e ammonium n i t r a t e a p p l i c a t i o n ) o r d a=a 1+a 2c a ( d e s c r i b e s weed d e n s i t y a t 2 and 46 days a f t e r ammonium n i t r a t e a p p l i c a t i o n ) . ** m = s l o p e ( b 2 o r a 2) f o r e i t h e r d j 8=b 1+b 2c^ ( d e s c r i b e s weed d e n s i t y a t 3 days b e f o r e ammonium n i t r a t e a p p l i c a t i o n ) o r d a=a 1+a 2c a ( d e s c r i b e s weed d e n s i t y a t 2 and 46 days a f t e r ammonium n i t r a t e a p p l i c a t i o n ) . *** p o f t h e r e g r e s s i o n e q u a t i o n = p o f b 2. § Average number o f days a f t e r ammonium n i t r a t e a p p l i c a t i o n . Data were c o l l e c t e d 31, 48, 49, and 50 days a f t e r a p p l i c a t i o n f o r b l o c k s 1, 2, 3, and 4 r e s p e c t i v e l y . -104-A p p e n d i x 2. R e l a t i v e s u s c e p t i b i l i t y o f weed s p e c i e s i n 1989. R e g r e s s i o n a n a l y s i s o f weed numbers b e f o r e and a f t e r ammonium n i t r a t e a p p l i c a t i o n . Weed Days* * a ** m R 2 S h e p h e r d ' s - p u r s e -2 21.16 0.21 0.01 0.680 +4 26.36 -1.29 0.48 0.001 +12 22.42 -1.11 0.44 0.001 Corn S p u r r y -2 20.47 0.32 0.04 0.411 +4 25.07 -0.65 0.14 0.105 +12 19.80 -0.90 0.32 0.010 Cudweed -2 119.66 -2.38 0.08 0.233 +4 110.95 -5.40 0.43 0.002 +12 68.13 -3.67 0.55 0.000 L a m b ' s - q u a r t e r s -2 23.67 -0.03 . 0.00 0.936 +4 24.58 -0.07 0.00 0.825 +12 23.11 -0.01 0.00 0.976 T o t a l -2 202.19 -1.87 0.05 0.361 +4 205.00 -7.98 0.57 0.000 +12 142.58 -5.69 0.73 0.000 Weed d e n s i t i e s ( p l a n t s m 2 ) b e f o r e ammonium n i t r a t e a p p l i c a t i o n were f i t t e d t o t h e model d =b +b c ( E q u a t i o n 3 d e s c r i b e d on p . 4 4 ) . Weed d e n s i t i e s e 1 2 P v ^ r / ( p l a n t s n f 2 ) a f t e r ammonium n i t r a t e a p p l i c a t i o n were f i t t e d t o t h e model d a=a i+a 2c a ( E q u a t i o n 4 d e s c r i b e d on p . 4 5 ) . There were f o u r r e l i c a t e s p e r ammonium n i t r a t e t r e a t m e n t ( 0 , 7.5, 10, 15 and 20 p e r c e n t N). C o n t i n u e d on n e x t page. -105-Days b e f o r e (-) and a f t e r (+) ammonium n i t r a t e a p p l i c a t i o n . a = dependent v a r i a b l e i n t e r c e p t ( b i o r a ^ f o r e i t h e r d ^ b ^ b ^ ( d e s c r i b e s weed d e n s i t y a t 2 days b e f o r e ammonium n i t r a t e a p p l i c a t i o n ) o r d a=a +a c ( d e s c r i b e s weed d e n s i t y a t 4 and 12 days a f t e r ammonium n i t r a t e a p p l i c a t i o n ) . m = s l o p e (b o r a ) f o r e i t h e r d =b +b c ( d e s c r i b e s weed d e n s i t y a t 2 days b e f o r e ammonium n i t r a t e a p p l i c a t i o n ) o r d = a + a c ( d e s c r i b e s weed d e n s i t y a t 4 and 12 days a f t e r ammonium n i t r a t e a p p l i c a t i o n ) . p o f t h e r e g r e s s i o n e q u a t i o n = p o f b . -106-A p p e n d i x 3. S h e p h e r d ' s - p u r s e d e n s i t y and weed c o n t r o l e x p e r i m e n t . R e g r e s s i o n a n a l y s i s o f s h e p h e r d ' s - p u r s e numbers a f t e r ammonium n i t r a t e a p p l i c a t i o n . Y e a r Days* n R 2 P %SPC* 1987 2 0.083 0.70 0.007 92 14 0.103 0.64 0.041 90 1988 2 0.150 0.70 0.002 85 15 0.236 0.71 0.008 76 22 0.221 0.72 0.010 78 S h e p h e r d ' s - p u r s e d e n s i t y ( p l a n t s n f 2 ) a f t e r ammonium n i t r a t e a p p l i c a t i o n was f i t t e d t o t h e model d f=n(d.) ( E q u a t i o n 6 d e s c r i b e d on p . 4 6 ) . f Days a f t e r ammonium n i t r a t e a p p l i c a t i o n . The r e g r e s s i o n e q u a t i o n s were used t o c a l c u l a t e p e r c e n t s h e p h e r d ' s - p u r s e c o n t r o l (%SPC) ( E q u a t i o n 7 d e s c r i b e d on p.47) f o r d i f f e r e n t days a f t e r ammonium n i t r a t e a p p l i c a t i o n . %SPC a t t h e s e d i f f e r e n t days was c o n s t a n t i r r e s p e c t i v e o f t h e i n i t i a l weed d e n s i t y . -107-A p p e n d i x 4. S h e p h e r d ' s - p u r s e d e n s i t y and weed c o n t r o l e x p e r i m e n t . R e g r e s s i o n a n a l y s i s o f b r o c c o l i growth and y i e l d . D ata Year Days* R 2 P Dry Wts 1987 * 0 0.29 0.000 0.01 0.643 7 1.61 0.000 0.04 0.360 14 5.17 -0.002 0.05 0.281 21 17.48 -0.005 0.05 0.290 28 42.08 0.007 0.02 0.512 1988 * 0 0.92 0.000 0.00 0.896 7 3.72 0.000 0.00 0.859 14 11.66 -0.001 0.02 0.572 21 35.25 -0.011 0.20 0.030 28 52.78 -0.003 0.00 0.773 Y i e l d 1987 7933 -1.71 0.02 0.560 1988 7805 -1.25 0.03 0.410 Head Wt 1987 797 -0.19 0.15 0.063 1988 632 -0.09 0.03 0.454 B r o c c o l i d r y w e i g h t (g p l a n t l ) , y i e l d (g p l o t 1 ) , and ave r a g e head w e i g h t (g p l a n t " 1 ) were f i t t e d t o t h e model y=q i+q 2d. ( E q u a t i o n 8 d e s c r i b e d on p . 4 7 ) . f Days a f t e r ammonium n i t r a t e a p p l i c a t i o n . * The day o f t h e ammonium n i t r a t e a p p l i c a t i o n , but j u s t b e f o r e s p r a y i n g . - 1 0 8 -Appendix 5. R e l a t i v e s u s c e p t i b i l i t y of crop c u l t i v a r s i n 1987. Regression a n a l y s i s o f c u l t i v a r dry weights a f t e r ammonium n i t r a t e a p p l i c a t i o n . C u l t i v a r Cone.* r l r 2 r 3 R2 P 'Emperor' 0 -0.27 0. ,103 -0.001 0.98 0.000 10 -0.26 0. ,107 -0.001 0.98 0.000 15 -0.24 0. ,101 -0.001 0.98 0.000 20 -0.34 0. ,090 -0.001 0.99 0.000 'SGI' 0 -0.48 0. ,127 -0.002 0.97 0.000 10 -0.46 0. ,115 -0.001 0.99 0.000 15 -0.48 0. ,107 -0.001 0.99 0.000 20 -0.38 0. ,078 N.S. 0.96 0.000 'Matra' 0 -1.52 0. .136 -0.002 0.96 0.000 10 -1.40 0. .139 -0.002 0.97 0.000 15 -1.23 0. ,094 N.S. 0.96 0.000 20 -1.38 • 0. .094 N.S. 0.97 0.000 ' El gon' 0 -1.03 0. .117 -0.001 0.96 0.000 10 -0.90 0. .109 -0.001 0.97 0.000 15 -0.85 0. .095 -0.001 0.99 0.000 20 -0.80 0. .080 N.S. 0.98 0.000 ' E a r l y M arvel' 0 -0.50 0. .110 ' -0.001 0.97 0.000 10 -0.50 0. ,118 -0.001 0.98 0.000 15 -0.50 0. .114 -0.001 0.96 0.000 20 -0.42 0. .115 -0.001 0.98 0.000 'Lunet' 0 -0.53 0. .112 -0.001 0.98 0.000 10 -0.41 0. .094 -0.001 0.98 0.000 15 -0.40 0. .100 -0.001 0.99 0.000 20 -0.43 0. .080 N.S. 0.99 0.000 'White L i s b o n ' 0 -1.98 0, .064 N.S. 0.96 0.000 10 -2.05 0, .064 N.S. 0.97 0.000 15 -1.93 0, .063 N.S. 0.96 0.000 20 -2.00 0, .060 N.S. 0.95 0.000 C u l t i v a r dry weight (g p l a n t " ) was f i t t e d t o the model l o g ( y ) = r 1 + r 2 x + r 3 x or l o g ( y ) = r 1 + r 2 x (Equation 9 and 10 d e s c r i b e d on p.64 and 65). f Ammonium n i t r a t e (percent N) a p p l i e d . N.S. = Not s i g n i f i c a n t (p<0.05). -109-Appendix 6. Relative susceptibility of crop cultivars in 1988. Regression analysis of cultivar dry weights after aimtonium nitrate application. Cultivar Cone.* r l R2 P 'Emperor' 0 0.88 0.055 0.91 0.000 10 0.75 0.058 0.85 0.000 15 0.92 0.043 0.93 0.000 20 0.83 0.053 0.87 0.000 'SGI'* 0 10 15 0.80 0.049 0.64 0.000 0.52 0.075 0.85 0.000 20 0.50 0.078 0.92 0.000 'Matra' 0 0.64 0.063 0.94 0.000 10 0.49 0.048 0.80 0.000 15 0.68 0.044 0.85 0.000 20 0.60 0.044 0.78 0.000 'Elgon' 0 0.21 0.066 0.80 0.000 10 0.27 0.050 0.75 0.000 15 0.16 0.069 0.90 0.000 20 0.28 0.060 0.84 o.ooo 'Early Marvel' 0 0.58 0.060 0.81 0.000 10 0.62 0.057 0.86 0.000 15 0.67 0.049 0.79 0.000 20 0.54 0.063 0.86 0.000 'Lunet' 0 0.65 0.052 0.92 0.000 10 0.62 0.051 0.79 0.000 15 0.69 0.054 0.84 0.000 20 0.60 0.066 0.99 0.000 'White Lisbon' 0 -1.30 0.046 0.76 0.000 10 -1.46 0.057 0.79 0.000 15 -1.31 0.056 0.86 0.000 20 -1.27 0.047 0.85 0.000 Cultivar dry weight (g plant *) was fitted to the model log(y)=r1+r2x+r3x or log(y)=r1+r2x (Equation 9 and 10 described on p.64 and 65), but r^ was not significant (p<0.05) for any of the treatments. f Ammonium nitrate (percent N) applied. i * Only three replicates of 0, 15, and 20 percent N were used for 'SGI' in 1988. I -110-A p p e n d i x 7. R e l a t i v e s u s c e p t i b i l i t y o f c r o p c u l t i v a r s . R e g r e s s i o n a n a l y s i s o f c r o p y i e l d p e r p l o t . Y e a r C u l t i v a r S 2 R 2 P 1987 'Emperor' 8.48 -0.026 0.02 0.610 'SGI' 4.43 0.012 0.01 0.784 'M a t r a ' 11.22 -0.041 0.05 0.407 ' E l g o n ' 10.09 ^0.121 0.21 0.075 ' E a r l y M a r v e l ' 10.64 -0.005 0.00 0.932 'Lun e t ' 17.76 0.128 0.16 0.126 'White L i s b o n ' 0.56 -0.004 0.04 0.491 1988 'Emperor' 8.50 0.045 0.02 0.564 'SGI'* 2.78 -0.006 0.01 0.775 'Ma t r a ' 14.81 -0.136 0.12 0.180 ' E l g o n ' 6.32 0.032 0.01 0.725 ' E a r l y M a r v e l ' 5.06 0.086 0.14 0.153 'Lunet' 6.58 -0.016 0.03 0.528 'White L i s b o n ' 1.12 -0.005 0.01 0.729 Crop y i e l d (kg p l o t " 1 ) was f i t t e d t o t h e model y=s i+s 2c ( E q u a t i o n 12 d e s c r i b e d on p. 6 5 ) . On l y t h r e e r e p l i c a t e s o f 0, 15, and 20 p e r c e n t ammonium n i t r a t e were used f o r 'SGI' i n 1988. - I l l -A p p e n d i x 8. R e l a t i v e - s u s c e p t i b i l i t y o f c r o p c u l t i v a r s . R e g r e s s i o n a n a l y s i s o f y i e l d p e r p l a n t . Y e a r C u l t i v a r S 2 R 2 P 1987 'Emperor' 678 -6.16 0.20 0.083 'SGI' 359 3.75 0.01 0.246 'Ma t r a ' 1190 -9.22 0.23 0.060 ' E l g o n ' 1048 9.87 0.18 0.103 ' E a r l y M a r v e l ' 814 3.48 0.04 0.484 Lunet 'White L i s b o n ' 14.19 -0.18 0.23 0.063 1988 'Emperor' 663 3.15 0.02 0.601 'SGI'* 470 0.88 0.01 0.784 'Ma t r a ' 1243 -11.72 0.09 0.248 ' E l g o n ' 599 4.63 0.02 0.592 ' E a r l y M a r v e l ' 415 2.95 0.03 0.508 'Lun e t ' 615 -3.12 0.08 0.282 'White L i s b o n ' 11.09 0.07 0.03 0.556 Crop y i e l d 1 (g p l a n t - 1 ) was f i t t e d t o t h e model y=s i+s 2c ( E q u a t i o n 12 d e s c r i b e d on p.65) * O n l y t h r e e r e p l i c a t e s o f 0, 15, and 20 p e r c e n t ammonium n i t r a t e were used f o r 'SGI' i n 1988. § Number o f 'Lunet' p l a n t s h a r v e s t e d was n o t r e c o r d e d i n 1987. 

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