Charcoal rot is a soilborne disease which was first identified and confirmed in NY in 2012. The disease is favored by hot, dry conditions. The fungus has a very wide host range, with more than 500 crop and weed hosts, including corn. The fungus produces microsclerotia as its primary survival structure, and is long-lived in the soil or on host residues. These microsclerotia germinate and infect soybean roots. The pathogen then colonizes the vascular system and is translocated throughout the plant, where it produces more microsclerotia which clog the plant’s vascular system, inhibiting its ability to uptake water. Symptoms usually occur during reproductive stages in infected plants as wilting and chlorosis followed by necrosis of the foliage. Dead leaves remain attached to the plants.
The fungus often produces copious amounts of microsclerotia in the dead tissues, which may be visible, appearing as a charcoal-like dust.
The fungus forms blueish-black streaks in the taproot and crown, which may be visible when split. The fungus can infect developing seeds and then be seed transmitted, possibly resulting in seedling death. Foliar fungicides are not effective against charcoal rot and are not recommended.
Rotation with non-host crops, including small grains is recommended to reduce pathogen populations in infested fields.