Downy Mildew
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Downy Mildew  Downy mildew, caused by a range of fungi and probably causes more damage to cucurbits than any other disease, particularly during extended periods of cool, moist weather. The disease is generally a problem from mid to late season and most prevalent in hot humid conditions.. Late season symptoms of downy mildew may easily be mistaken for early senescence due to other factors. Susceptible Plants- Cucurbits family, lettuces, onions, berries, as well as many other plants, particularly when young. . Symptoms- Downy mildew symptoms occur on cucurbit leaves but not other plant parts. The older leaves nearest the center of the hill are usually affected first. On cucumber, the disease first appears as angular, yellow spots on the upper leaf surface. Spots are often bounded by the leaf veins. During humid weather a grayish growth of the fungus appears on the undersides of these spots. Spores are produced in profusion in these areas. On watermelon and cantaloupe, leaf spots are at first yellow but later appear somewhat darker than the spots on cucumber. Spots enlarge and a general yellowing of the leaf, followed by brown discoloration and, finally, death of the entire leaf occurs. During rainy or humid weather, this progression may occur rapidly. Death of the leaves exposes fruit to sun scald. In some years the disease may destroy entire plantings of susceptible plants. Prevention and Control- Grow resistant lettuces such as ‘Sangria’ or ‘Little Gem’. Use a 5 year crop rotation for onions where downy mildew has occurred. Improve ventilation and air flow. Remove infected leaves or individually affected plants. If the downy mildew continues remove and destroy all infected plants. Provide adequate plant spacing to reduce the density of the canopy and minimize humidity. Avoid overhead irrigation, which lengthens the duration of leaf wetness and favors downy mildew. Fungicidal Control- Mancozeb Fungicide
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