Powdery mildew (Blumeria graminis)

Powdery mildew: biology

Powdery mildew in soybeans is most noticeable when conditions are wet or humid. It develops on the leaves, usually in August and September. Outbreaks arise when disease symptoms begin in early July and the environmental conditions remain cool, cloudy and humid through to pod fill.

Although powdery mildew occurs in most fields, it is considered a minor disease and economically insignificant.

Powdery mildew appears as a white powdery growth of the mildew fungus on the upper surface of the leaf; the soybean seeds themselves do not become infected.