Issue No. 21, Article 6/September 9, 2011
Be on the Lookout for Charcoal Rot in Dry Areas
Symptoms of charcoal rot, caused by the soilborne fungus Macrophomina phaseolina, are apparent in soybean fields located in areas of the state that have been hot and dry. Symptoms in affected fields appear as individual plants or patches of wilted and dead plants. Gray to black "specks" will be apparent on the lower stems of affected plants when the epidermis is shaved off with a knife. These specks, known as microsclerotia, are the survival structures of M. phaseolina.
A soybean field with plants affected by charcoal rot.
Dark specks (microsclerotia) can be observed inside the lower stems of soybean plants affected by charcoal rot.
Management of charcoal rot requires an integrated approach. Although no soybean varieties have complete resistance, varieties can differ in their levels of susceptibility to the disease. Macrophomina has a wide host range, which includes corn, sorghum, and sunflower, so crop rotation alone may 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. Foliar and seed treatment fungicides do not provide protection against charcoal rot.--Carl A. Bradley
Carl A. Bradley