Lesions which form on the lower leaf surface tend to be more diffuse. Fruit infections begin as sunken brown spots and may later develop a dark powdery appearance as the fungus sporulates. The infection may also begin at the blossom end with the entire fruit eventually turning brown and shriveling. The fungus survives the winter in infected crop debris as mycelium and may also survive on seed. The overwintering fungus serves as the source of primary infections and spores from these infections cycle the disease through the growing season.
Spores are readily wind-blown and splashed by rain.
Periods of wet weather are necessary for abundant spore production. Fall plowing will bury the remaining debris and promote its breakdown. Rotations which exclude cucurbits for 1-2 years may be beneficial. Some resistant varieties are available. Fungicide treated disease-free seed may be helpful.