Charcoal rot of corn
Charcoal rot is caused by the fungus Macrophomina phaseolina. The pith and rind of affected plants appear gray because of the numerous tiny black microsclerotia that develop. The pith tissue is disintegrated, leaving the vascular tissue with a granular, gray appearance.
The fungus overwinters as sclerotia in crop residue and soil and infects plants through roots. It may occur when growing conditions are hot and dry.
Crop rotation is usually not effective because sclerotia can survive more than one year in soil, and other crops such as soybean and alfalfa are hosts. Numerous microsclerotia produce the "charcoal-like" appearance of tissue characteristic of charcoal rot. Image: G. Munkvold
Charcoal rot causes disintegration of pith tissue as well as formation of microsclerotia. Image: G. Munkvold