Probably the most common disease in soybeans is brown spot, also known as Septoria brown spot. It is a fungal disease caused by the pathogen Septoria glycines. It is very common across the Corn Belt and appears in about all soybean fields to some degree. The disease is usually present in the lower canopy, but can move upwards if weather is warm and moist.

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This pathogen overwinters and survives in soybean residue and can survive over a 2-year corn-soybean rotation. When it rains, the spores splash up into the lower canopy and infect lower leaves. According to the NCSRP Soybean Research Initiative “Septoria brown spot generally infects older leaves in the lower canopy. However, during a warm, rainy season, the disease may move up through the plant. Later in the growing season, infected leaves may turn rusty brown or yellow and drop prematurely.”

What does it look like? According to the NCSRP post “Symptoms of brown spot are many small, irregular, dark brown spots on both the upper and lower leaf surfaces. Adjacent spots (lesions) frequently merge to form irregularly shaped blotches and browning of the leaf edges or along the leaf vein. Infected leaves turn brown and yellow and may drop prematurely.” This disease is common but primarily seen in the more humid lower canopy. If weather remains warm and dry it will stay put below.

Image Courtesy of North Central Soybean Research Program (NCSRP)

Management is simple because the disease is rarely an economic threat:

• Rotate soybeans with small grains or corn to allow soybean residue to decay.
• Manage residue, especially in fields with high levels of brown spot.
• As a minor disease that rarely impacts yield fungicide isn’t warranted.

However, if you spray for other foliar diseases, brown spot will also be kept in check. And Bayer CropSciences recently revised its ILeVO^® label and added control of Septoria brown spot.

Eric Ifft, customer care representative with Bayer CropSciences in Illinois stated in his weekly email “ILeVO seed treatment is now labeled for Septoria Brown Spot, and this week I saw fields where ILeVO control of this fungal disease was very evident. I was in several fields this week where the growers had the same soybean variety with and without ILeVO, and when you pulled back the canopy, there was significantly less Septoria in the ILeVO-treated soybeans.”

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.