Late blight of potato management11/3/2023 Plants that are severely affected by late blight have a distinctive odor as a result of the rotting leaf and stem tissue. Lesions on the stems appear water-soaked and are dark green to black in color. The outer margin of the lesion is surrounded by a pale green to yellow border. Under the cool, moist conditions of early morning, a grayish-white mildew comprised of fungal mycelium and spores develops on the under-surface of the lesions. These spots are not limited by leaf veins as with early blight. Under favorable, cool, moist weather conditions, the spots rapidly enlarge into dark brown spreading spots. The first symptoms of late blight are small, light green, water-soaked spots that usually develop on the lower leaves. Field infestation of late blight Symptoms Attempting to use any fungicide to eradicate the disease after it is well established promotes the selection and spread of new fungicide resistance.įigure 1. Cultural practices are the first line of defense, and forecasting techniques and proper application technology are essential for efficient, targeted applications of fungicides.Īll fungicides, old or new, must be used as protectants before late blight is established in the crop. Since, late blight is a community disease, for effective control integrated management MUST be adopted by all producers, large and small, including organic farmers, home gardeners and other specialized growers by pesticide and equipment manufacturers and suppliers and by government agencies, extension specialists and crop consultants.įungicides cannot be used alone for effective control of late blight, but must be used as one tool in an integrated management strategy. In the past few years has resulted in new, more aggressive strains of the fungus, some of which are fungicide-resistant. In recent years, significant changes in isolates of late blight fungus have been recorded, including changes in agressiveness to potato and tomato plants, optimal temperature range and also sensitivity to metalaxyl fungicide. Late blight has been a problem for potato growers in North America since the 1840s. Integrated Management of Late Blight in Potatoes Introduction
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