Leaves show signs of stress turning reddish and finally gray powdery as fungus sporulates. Leaves are chlorotic and drop. Mycelium is dikaryotic and overseasons as ascopores on buds and fallen leaves. Grow intercelluarly no haustoria and cause great cell enlargement. White to grey powdery mildew on both sides of the leaf occurring during dry weather.
Whitish mycelium can cover the whole plant and the plant eventually becomes yellow to necrotic.
Tiny Cleistothecia begin as white pin points develop into black cleistothecia in older necrotic tissue late in the season. Overseasons as cleistothecia and mycelium in plant debris. There are only about 6 genera of Powdery mildews which cause economic damage. These can be identified by the structure of the cleistothecial appendages. Occurs worldwide and shows an example of physiologic specialization.