Charcoal rot, also known as summer wilt or dry weather wilt, has recently been reported to be in Illinois soybean fields, says Dean Malvick, University of Illinois Extension.

Although the recent rains in much of the state may have significantly alleviated the potential damage from this disease, a return to dry and hot conditions may favor more development of charcoal rot.
Charcoal rot is typically more common across southern than northern and central Illinois, but it can occur anywhere in the state where plants are stressed, especially because of hot and dry weather. The most seriously affected areas are often in the drier parts of fields.

Look for several characteristics for diagnosis. Leaves of severely infected plants turn yellow and brown, wilt, and stay attached to the plant. The initial yellowing is usually more uniform across the leaf than that caused by sudden death syndrome or brown stem rot. A more clear diagnosis is based on the appearance of the root and lower stem. Scrape off the surface of both with a fingernail or knife, and look on and under the epidermis. Plants infected with charcoal rot will have tiny gray-black specks called microsclerotia, which appear similar to scattered bits of charcoal dust. They are difficult to see without the help of a hand lens. If the root and lower stem are cut, there are often wavy gray to black streaks inside the root and lower stem.

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