- Charcoal rot occurs primarily in dry, hot conditions. This disease can cause minor to significant yield losses, and it is most common in the southern areas of the Midwest.
- Macrophomina phaseolina is a fungus that has a wide host range that includes corn, wheat, and some weeds. The fungus overwinters in dry soil or residue of host tissues, and it can be spread with contaminated seed.
- Symptoms typically occur during or after flowering.
- Brown lesions may form on the hypocotyls or emerging seedlings.
- Leaflets may be small and ultimately wilt and turn brown.
- The taproot and lower stem may become light gray.
- Small black dots may form beneath the epidermis of the lower stem and in the taproot to give the stems and roots a charcoal-sprinkles appearance.
- In addition, reddish-brown discoloration and black streaks can form in the pith and vascular tissues of the root and stem.
Time of Occurence
- Seedlings may be affected in hot, dry soils in early summer, but the disease typically appears after mid-season.
Conditions Favoring Disease
- Hot, dry weather
- The disease is most severe where plants have been growing under conditions of stress or injury.
- Choose soybean varieties that express moderate resistance to this disease.
- Manage fields to avoid drought stress.
- Decreased disease has been reported with minimal tillage, perhaps due to cooler soils and less moisture stress.
- Crop rotation with cereals or corn for 2 to 3 years may be beneficial.