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Powdery mildew Photo Identification

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  • Pest Type: Disease
  • Crops Affected: Cereals, Small Grain, Wheat, winter, Wheat, spring, Wheat, Soybeans, Barley, Peas
  • Scientific Name: Erysiphe spp.
Powdery white spots appear on leaves when the plants are flowering and, under rain-free conditions spread rapidly to cover all leaves, stem, tendrils and pods. As foliage ages, pinhead-sized overwintering bodies of the pathogen speckle the mildewed surface. Powdery mildew is often most conspicuous on late maturing crops or groups of plants. Plants affected by powdery mildew are usually in parts of the field where growth is dense and the air moist - these are the conditions preferred by this fungus. Small irregular or circular gray-white spots appear on the upper surfaces of leaves. Those spots enlarge as the fungus grows, and the spots take on a floury appearance due to the production of an enormous number of spores. The lower surfaces of leaves beneath the diseased spots turn yellow and the older parts of spots turn brownish. Grayish-white spots will also generally be found on spikelets. Small black fruiting bodies form in mature lesions. Under very favorable conditions, powdery mildew spots can also develop on stems and heads. Severe infestations cause infected leaves to wither and die early.

Disease Cycle
Seed transmission has not been proven and it is uncertain whether the overwintered bodies can release viable spores. Rapid spread is due to prolific production of wind-blown spores that can infect without rain or dew. These airborne spores land on plant surfaces, germinate, and penetrate the epidermal cells. In southern areas, it may overwinter on living leaves of various plant species. Spread of this fungus is favored by cool weather, not above 86F.

Control Measures
In many areas, this disease is present every year. Resistant varieties have been developed for areas where powdery mildew is most serious. Crop rotation also helps. Because of the superficial type infection, foliar fungicides are generally very effective. If powdery mildew develops in your area, discuss control options with local advisers. is your source for ag news and information on crop pest identification, commodity and market prices, agricultural news & issues, and access to crop production management tools such as crop yield & planting calculators and herbicide, fungicide, and weed control information.