Affected leaves may turn completely yellow, die, fall off, and exposed fruit beneath may become sunburned. Severely infected plants may have reduced yields or shortened production times.
New growth is dwarfed, distorted, and covered with a white, powdery growth.
Grapes may also crack or split as they continue to grow and expand after a severe mildew infection. All powdery mildew fungi require living plant tissue to grow. On perennial hosts such as grapes, raspberries, roses, and fruit trees, powdery mildew survives from one season to the next in infected buds or as fruiting bodies called cleistothecia, which reside on the bark of cordons, branches, and stems. On strawberries the disease can survive on leaves that remain on the plants through winter. Year-round availability of crop or weed hosts is important for the survival of the powdery mildew fungi that infect cole crops, tomatoes, peppers, and eggplants.