- any of an order (Erysiphales) of ascomycetous fungi that are parasites on the surfaces of higher plants and produce closed fruiting bodies in a powdery mass
- a plant disease caused by a powdery mildew
powdery mildewpowdery mildew
- Any of various plant diseases caused by fungi, especially of the family Erysiphaceae, that produce powdery conidia on the host surface.
- A fungus causing such a disease.