Powdery mildew of soybean
Powdery mildew is caused by the fungus Erysiphe diffusa. The most common and characteristic sign of powdery mildew is white, powdery fungal growth that can cover all aboveground plant parts, particularly the upper leaf surface. Later symptoms may include plant tissue yellowing and premature defoliation.
Powdery mildew usually does not appear until mid- to late reproductive stages of the crop and can be more severe in late-planted soybeans. The fungus survives in infested crop residue and favorable conditions include cool, cloudy weather and low humidity.
Most commercial soybean varieties are resistant. Fungicides effectively manage powdery mildew; however, limited situations exist where fungicide use will be profitable. Early powdery mildew on soybean leaves. Image: C. Grau
Powdery mildew appears as a white, powdery fungal growth on soybean plant tissue. Image: D. Mueller