Powdery Mildew

Guy Padgett  |  8/19/2011 11:32:33 PM

Powdery mildew.

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Powdery Mildew (Microsphaera diffusa)
Daniel V. Phillips
University of Georgia

Powdery mildew occurs sporadically on soybeans. Yield reductions are possible if foliage is affected during pod fill or extensive defoliation occurs. Plants are susceptible at any growth stage, but symptoms are rarely seen in the field until the mid to late reproductive stages. Disease incidence is greater in seasons with cooler than normal temperatures.

The first symptom is usually a circular area of white to light-gray, superficial powdery growth on the upper leaf surface. Under favorable conditions, cool humid nights and mild dry days, these areas expand rapidly, coalesce and cover the entire leaf surface. All green plant parts may be covered by the powdery growth. Heavily infected leaves turn yellow, then brown, and drop prematurely.

Powdery mildew is controlled with resistant cultivars. Most determinate soybean cultivars are highly resistant to powdery mildew, while many indeterminate cultivars are susceptible.

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