Powdery Mildew

Powdery mildew is always caused by fungi. A distinction is made between powdery mildew and downy mildew.

Powdery mildew spreads mainly during warm, dry summer weather—it is considered a “fair-weather” fungus—and is caused by ascomycetes. It can be recognized by a white coating on the upper surface of the leaves that can be wiped off.

Powdery mildew is caused by fungi known as oomycetes. A white-gray coating forms on the underside of the leaves and cannot be wiped off. It tends to occur in wet and humid weather.