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A flagging disease of western white pine Molnar, Alexander Charles

Abstract

A disease, causing severe flagging of young western white pine (Pinus monticola Dougl.), was investigated at Hill Siding and Arrow Park, British Columbia. The primary symptom of the disease was flagging of twigs, resulting from a rapid necrosis of terminal shoots and less commonly from girdling-lesions on 2-year-old growth. A small percentage of the severely flagged trees died. Damaging effects of the disease were confined to trees under 40 years of age and to stand forms with a higher than average component of white pine in the susceptible age class. Efforts to isolate the causal fungus yielded 22 fungi in culture, only two of which occurred with sufficient frequency to warrant further study, an unknown fungus "B” and Pullularia pullulans (deBary) Berkhout. A search for fructifications associated with the disease revealed apothecia of a Tympanis, very similar to those of Tympanis pithya (Karst.) Karst., to be associated with 16 per cent of a random sample of 425 flagged twigs. The pycnidia of the imperfect stage of Tympanis sp. occurred less commonly. Spore cultures from Tympanis apothecia were different from those of any of the 22 fungi isolated in tissue culture and it seemed probable that Tympanis occurred as a pioneer saprophyte on killed twigs. External signs of Pullularia pullulans occurred commonly in the form of erumpent sclerotia, and external hyphae with resting spores. A scale insect, resembling Matsucoccus sp., was found at a high infestation level in one stand and less commonly in the remaining stands. Reasons for discounting the insect as a primary causal agent of flagging are outlined. Field inoculations with Pullularia pullulans and greenhouse inoculations with Pullularia pullulans and the unknown fungus "B" produced questionable results with the latter fungus, but indicated Pullularia pullulans to be pathogenic under the conditions imposed by the experiment. Results of inoculation experiments are snmmarized in four tables. The historical background and cultural description of Pullularia pullulans is outlined. Experimental and observational evidence suggests that the fungus is one of the causal agents, and probably the primary agent for the flagging. On the basis of the limited damage caused by the flagging and the sporadic occurrence of the susceptible stand form, control measures are deemed unwarranted.

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