Soybean Disease Management

William Hogan  |  7/7/2011 6:15:02 PM

The year 2011 has been a strange and challenging year to try to produce a soybean crop. As usual, the weather is the culprit. Everyone has experienced the effects of the drought. We have talked about the effects of the dry conditions on all crops, livestock, and gardens. All this talk hasn’t helped the situation. Only a general, consistent supply of rainfall will remedy the problem. Until then, we wait and do the best we can with the conditions we have. Managing foliar disease is something we can do.

Early planting, delayed planting and delayed growth (the last two caused by drought) have given us a soybean crop that is quite varied in maturity for this time of season. Each individual field has to be scouted and specific management decisions made for it. As our soybean crop progresses into the reproductive maturity stages (flowering through pod fill) the management of foliar diseases becomes essential. These maturity stages are the most critical to grain yield. They are also the most susceptible stages to disease development. Producers should scout their fields regularly for signs of disease development.

Asian Soybean Rust can be a devastating disease. It was not an economic factor last season. It has not been prevalent this season. However, the potential for its development exists. Don’t take for granted that your crop is not at risk. ASR is usually detected as small, brown lesions on the bottom side of the soybean leaf. These are most numerous on the lower leaves and in areas of the leaf that hold surface moisture (along leaf veins). ASR lesions can be confused with other fungal and bacterial leaf spots. The use of a hand lens and experience in recognizing the disease are necessary for accurate, early detection. If the disease is present and the soybean plants are in the bloom stage or a later maturity stage, an application of a labeled triazole fungicide is recommended. There are several triazole fungicides that have proven effective at inhibiting the development of ASR in infected plants. Strobilurin fungicides are recommended for protecting the soybean plant from ASR infection.

Strobilurin fungicides also offer excellent protection from aerial blight. Aerial blight has been one of our most costly diseases. It is also one of our most common soybean diseases. Since these two types of fungicides have different modes of action, applying a combination of a triazole fungicide with a strobilurin fungicide at the recommended rates has proven very effective in managing aerial blight and ASR.

Properly timed and at the recommended rate per acre this fungicide combination is an essential tool in managing two major soybean diseases. If neither disease is actively developing, the recommended time of application is between early pod set and early pod fill. This should give good protection during the critical grain development stages and inhibit undetected ASR infection. Don’t be tempted to cut back on rates per acre. Use the recommended rate of a fungicide or combination of fungicides.

If your soybean crop is worth carrying to harvest, it’s worth protecting. Do not neglect to manage disease.

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