Powdery Mildew - Identification photos.
Sam Freeman shows the underside (below) and top side (right) of powdery mildew found in Cabernet Sauvignon. Powdery mildew increases during spring from a small amount and spreads.
Fresh powdery has the appearance of a whitish film on the backs of leaves. New leaf growth is distorted and older leaves become blackened.
Powdery mildew spores are carried by air and, once active, will continue to spread in dry conditions.