Warnings and Advice About Cucurbit Downy Mildew

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Caused by the fungus-like oomycete pathogen Pseudoperonospora cubensis, cucurbit downy mildew can infect watermelon, pumpkin, squash, cucumber, and cantaloupe. The disease travels from warmer areas to ours and first shows as angular, yellow to brown lesions on top of the leaves, restricted by leaf veins. In moist conditions, the underside of these lesions may be covered in a dark fuzz or “down.”

Downy mildew on cucumber plant

To minimize Downy Mildew problems, scout plants often and remove infected plants, plant tolerant varieties when possible, keep leaves as dry as possible via wide plant spacing, tunnel structures, and drip irrigation only, and protect the crop with fungicides. Organic growers can rotate between fixed coppers, biofungicides, and potassium bicarbonate products, and conventional growers can add labeled fungicides such as chlorothalinil and mancozeb to their rotations. For more information about this and other crop management, call Cooperative Extension at 828-264-3061.