Michael A. Ellis Powdery mildew is an important disease of grapes throughout Ohio. The disease generally is considered less economically important in Ohio than black rot or downy mildew. However, uncontrolled, the disease can be devastating on susceptible varieties under the proper environmental conditions. Unlike black rot and downy mildew, the powdery mildew fungus does not require free water on the plant tissue surface to infect.
Powdery mildew can result in reduced vine growth, yield, fruit quality, and winter hardiness.
Varieties of Vitis vinifera and its hybrids generally are much more susceptible than American varieties. The powdery mildew fungus can infect all green tissues of the vine. The patches may remain limited throughout most of the season. Severely affected leaves may curl upward during hot, dry weather. Expanding leaves that are infected may become distorted and stunted.