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. Many grape varieties are affected. Fungal infection on leaves appears as whitish, powdery covering on upper and lower leaf surfaces. On fruit, the whitish powdery sporulation also appears.