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|downy mildew |
A disease of plants caused by oomycete organisms of the order Peronosporales and characterized by gray, velvety patches of spores on the lower surfaces of leaves. Downy mildew of the grapevine nearly destroyed the French wine industry in the 1870s, spurring the development of the first chemical pesticides used on plants.
disease of plants, especially in cool humid regions, caused by several fungi, including species of Basidiophora, Bremia, Peronospora, Phytophthora, Plasmopara, Pseudoperonospora, and Sclerospora. White, gray, bluish, or violet downy patches of mildew form mostly on the undersides of leaves in damp weather. Pale-green to yellow or brown areas usually develop on the upper leaf surface opposite the downy growth. Affected leaves often wilt, wither, and die early. Stems, flowers, and fruits are sometimes infected. Seedlings may wilt and collapse. Garden plants, bush fruits, vegetables, and certain trees, shrubs, field crops, and weeds are susceptible.