No. 22 Article 4/September 7, 2007

Charcoal Rot of Soybean

Many soybean fields in the dry portions of the state are being affected by charcoal rot, caused by the soilborne fungus Macrophomina phaseolina. Charcoal rot is a disease that can thrive under hot and dry conditions. Symptoms in fields currently affected in southern Illinois appear as patches of wilted and dead plants. In charcoal rot-affected plants, the pith of the lower stem contains tiny black structures, known as microsclerotia, that resemble charcoal dust. The microsclerotia are the survival structures of the fungus. When the epidermis of affected plants is removed, the area beneath the epidermis may have an ashy-gray appearance and contain black streaks.

A field in Gallatin County affected by patches of charcoal rot.

Discoloration of the internal stem caused by the charcoal rot fungus.

Management of charcoal rot requires an integrated approach. Although no soybean varieties have complete resistance to charcoal rot, varieties can differ in their levels of susceptibility. Because the charcoal rot fungus has a wide host range, including corn, crop rotation alone will not provide complete management. Practices that reduce drought stress may help, such as avoiding high seeding rates and using conservation tillage practices that conserve soil moisture. The foliar and seed treatment fungicides currently available do not provide protection against charcoal rot.--Carl A. Bradley

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