With the rainy weather in Tennessee it’s not surprising disease is developing in soybeans.  Specifically, southern blight and downy mildew have been reported.

While the rainy conditions have promoted downy mildew in many soybean fields it rarely affects yields and it is not recommended to apply a fungicide for it.  Similarly southern blight is usually a minor disease and in most situations it is unnecessary to implement any control measures.  There are some cultural control practices that can be implemented when necessary to limit the impact of southern blight, which include, rotate to non-host crops such as corn, milo, or pasture grasses; application of calcium and nitrogen fertilizers may decrease disease; and sanitation measures. Infected areas can be harvested last in order to reduce spreading the fungus to other areas of the field and tillage may reduce the population of the fungus in the soil.

Diseases that will most likely develop over the rest of the season in Tennessee include frogeye leaf spot (if a susceptible variety has been planted) and soybean rust.  Both these disease have a greater potential of decreasing yield, but can be managed properly with fungicides when needed (see previous articles: Scouting and Sampling Frogeye Leaf Spot in Soybean and Scouting for Soybean Diseases and Deciding on Fungicides and Application Timing ). Samples collected this week from middle Tennessee counties bordering Alabama have been negative for soybean rust.