Powdery mildew
Powdery mildew appears on the green bean plant as a powdery white mold on the surface of the green bean leaf. This can grow and cover the entire plant. Yield losses occur because the damage makes the crop not commercially viable. Powdery mildew can be controlled with applications of sulfur. The original trials in the 1930s showed that incidence could be reduced from 87% to 2%.