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Powdery mildew is caused by the fungi (in vine crops by Sphaerotheca fulginea & Erysiphe cichoracearum) that appear as a white powdery growth on the stems and leaves. It affects cucumbers, pumpkins, melons, ornamental gourds, squash, and other vegetables. The pathogen can be introduced by wind from areas with relatively warm climate where it overwinters. Disease development is very fast in three days and nights that are hot and dry during the day and the nights are cool with a high relative humidity. The pathogens attack the vines and lower surfaces of the leaves first. Small patches of white thin thread-like masses of mycelium appear on the infected areas. These spread and eventually cover the whole leaf surface or vines with white powdery looking fungus. The affected leaves turn yellow and finally dark brown causing an early death of the leaves, which affects fruit development. It does not affect the petioles. The disease tends to be a problem from late July to early September.

Plant resistant varieties of cucumbers, pumpkins, and muskmelons; follow a regular spray schedule with recommended fungicides in your state; rotate vine crops with non-cucurbit crops; and use cultural practices that avoid overcrowding, too much shading, and poor air circulation.