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Septoria brown spot causes small, angular to somewhat circular, red to brown spots on the unifoliolate and lower trifoliolate leaves. The individual spots can run together, forming irregularly shaped brown blotches on the leaves. Leaves quickly turn yellow and drop.
Progressing from lower to upper leaves, the pathogen is spread by wind-blown rain. It survives in crop debris and seeds. Septoria brown spot is common early in the season on unifoliolates; if weather conditions favorable for disease development occur later in the season, the disease may move through the plant canopy causing more serious symptoms and potential yield losses. Warm, wet weather favors infection and disease development. Dry weather usually halts the spread of brown spot. Crop rotation with at least one year between soybean crops is the main control for Septoria brown spot. |
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