Charcoal Rot of Soybean
The disease can develop at any growth stage but plants are most susceptible at the beginning of flowering. The symptoms are usually visible during long periods of warm, dry weather. Plants have low vigor, and they start to wilt during the hottest hours of the day, recovering partially during the night. Younger leaves start yellowing and pods remain unfilled. The rot in roots and stem is characterized by a reddish-brown grainy discoloration in the internal tissues. Randomly distributed black specks at the base of the stem is another symptom of the fungal growth.
Charcoal rot of soybean is caused by the fungus Macrophomina phaseolina. It overwinters in plant debris in the field or in the soil, and infects the plants via the root early in the season. Symptoms can remain latent until adverse environmental conditions (e.g. hot, dry weather) stress the plants. The damage caused to the root internal tissues impairs water uptake when the plants need it the most. Unlike other fungi, the activity and growth of the charcoal rot fungus are favored by dry soils (27 to 35°C).
You can try using the parasitic fungi Trichoderma spp. It parasitizes other fungi, among them Macrophomina phaseolina. Or use the bacterium Rhizobium sp. to control the fungus.
Always consider an integrated approach with preventive measures together with biological treatments if available. No fungicide seed or foliar treatments offer consistent control of charcoal rot.