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Ecology and Epidemiology

Overwinter Survival of Podosphaera clandestina in Eastern Washington. Gary G. Grove, Assistant plant pathologist, Washington State University Tree Fruit Research and Extension Center, 1100 N. Western Avenue, Wenatchee 98801; Robin J. Boal, research technologist, Washington State University Tree Fruit Research and Extension Center, 1100 N. Western Avenue, Wenatchee 98801. Phytopathology 81:385-391. Accepted for publication 30 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-385.

Podosphaera clandestina survived winter as cleistothecia on senescent cherry leaves on the orchard floor or trapped in tree crotches, as cleistothecia in partially decomposed leaves trapped in tree crotches, or as cleistothecia trapped in bark crevices. Ascocarp viability ranged from 55–90% in early February to 5–33% in mid-May. Inoculation of cherry seedlings with overwintered cleistothecia collected from early March through mid-May resulted in infection, with the largest number of mildew colonies resulting from inoculation with cleistothecia that were collected around bud burst. Ascospore release began 1 mo before bud burst and continued until after the bloom period. Trapping of ascospores and cleistothecia from the orchard air preceded the initial appearance of mildew colonies. Results of orchard surveys and experiments with dormant buds failed to provide evidence that P. clandestina survived winter as mycelium in dormant infected buds. Cleistothecia appear to be the principal source of primary inoculum for epidemics of sweet cherry powdery mildew in eastern Washington.