Brown Spot

Guy Padgett  |  8/19/2011 11:30:32 PM

Brown spot.

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Brown Spot (Septoria glycines)
Daniel V. Phillips
University of Georgia

Brown spot is a common disease which occurs frequently on young plants. If warm moist weather conditions continue, infection, and defoliation progress from lower to upper leaves. Usually the hot dry weather of mid-season arrests disease development, but the disease may become active again near maturity. If conditions favorable for disease development continue into the season or reoccur before maturity, the resulting defoliation can cause serious yield reductions. The pathogen overwinters on infected leaf and stem debris, and the disease is most severe when soybeans are grown continuously in the same field.

Cotyledons, primary leaves, and lower trifoliolate leaves typically show brown spot symptoms. The brown to red lesions vary in size from pinpoint to 1/15 inch wide, but may coalesce and form larger irregular shaped spots. Severely affected leaves turn yellow and drop.

Although there are differences in susceptibility of cultivars, no highly resistant cultivars are available. Control is best achieved by rotation and deep plowing to reduce disease incidence.

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