Watermelons and Downy Mildew

Jul 3, 2019

Hello Gardeners, I’m Amanda McNulty with Clemson Extension and Making It Grow. Certain strains of downy mildew are serious diseases of cucurbit family members  – squash, cucumbers, melons and watermelons. Watermelons, in particular, are very important economically for some South Carolina farmers. Infected plants have angular lesions on the tops of leaves but the reproductive structures, resembling a grey, white mold, are on on the underside of the leaves. To spread, these spores needs free water and cool temperatures – so the usually early morning time for irrigation makes infection more likely if you have overhead sprinklers and, of course, we can’t control rainfall. Unlike powdery mildew, this disease doesn’t have reproductive structures that live in dead plant material so it doesn’t overwinter in South Carolina unless it is on plants growing in greenhouses throughout the winter. In parts of Florida, year-round production of cucurbits keeps the disease-causing spores in circulation, and they travel north on wind currents.