The disease also affects tart cherries. Pathogen and Symptoms Cherry powdery mildew is caused by the fungus Podosphaera oxyacanthae . This fungus most commonly infects young, expanding leaves. The initial symptom of foliar powdery mildew is a light green, roughly circular lesion on either leaf surface. As the infection progresses, a white cotton-like growth develops on the infected area.
Infected leaves curl or blister, left.
A white, cottony growth covers surface of infected leaves, above right. Cleistothecia form as leaves and mildew colonies age, below right. Mildew appears as a round, slightly depressed area on fruit, left. Fungus may cover small areas, or entire fruit, right. Overwintering cleistothecium releases spores that result in primary infection in spring.