This species of powdery mildew overwinters on dead leaves on the orchard ground. New leaf infections may begin as soon as shoots elongate, but are usually first noticed in June. Infections become abundant in shady, humid areas with poor air circulation. Summer heat can discourage new infections, but often trees are vigorous and shady enough for the fungus to reproduce in mid-summer. Once spores collect at the base of stems on fruit, direct infection and damage will occur as the fruit ripens. When cool weather returns in late summer and early fall, new leaf infections can occur.
