Guy Padgett  |  8/19/2011 11:38:11 PM

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Alternaria (Alternaria spp.)
Daniel V. Phillips
University of Georgia

Alternaria leaf spot has been reported from all soybean growing areas. This fungus is often a secondary invader following mechanical injury, insect damage, or another disease. Alternaria leaf spot is a late season disease that develops on maturing leaves or on younger leaves if injured. If uninjured, most improved determinate cultivars appear to be resistant until leaves start to senesce. Since lesions develop after the onset of yellowing, yield losses are considered minimal. The causal agent appears to be seedborne.

Lesions are nearly circular unless they are restricted by a major vein or coalesce with another lesion. Single lesions range up to 1 inch in diameter, have brown concentric rings, and a well defined margin.

Control measures are not considered necessary.

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