Severe infection leads to defoliation. Infected fruit turn light brown to purple, then shrivel and detach easily. With high RH, white cottony sporulation will occur on fruit. Many grapes are susceptible to downy mildew, with Chardonnay, Riesling, Catawba, Delaware and Niagara highly susceptible. Lesions on shoots are most common, although leaves and fruit can become infected.
Elliptical lesions develop on the lower part of the shoot.
Eventually, the lesions coalesce, resulting in black crusty areas which may cause the shoot to split. On leaves, lesions begin as light green and irregular in shape. Heavy infections cause leaves to become misshapen, turn yellow, and drop off. Phomopsis infections seem to be less common during the hot weather of the growing season, thus the vine is susceptible primarily early and late in the season. Although not a major disease problem, it can potentially become a problem in the future.