Edward J. Sikora, Extension Plant Pathologist, Associate Professor, Plant Pathology, Auburn University Plant Disease Notes Black Rot of Sweet Potatoes Black rot is caused by the fungus Ceratocystis fimbriata. The disease can cause significant losses during storage, in the transplant bed, and in the field. The pathogen not only reduces yield and quality but also gives the sweet potatoes a bitter taste. Small, circular, slightly sunken, dark brown spots are the initial symptoms of black rot.
Spots enlarge and appear greenish black to black when wet and grayish black when dry.
The rot usually remains firm and shallow. However, if secondary fungi or bacteria invade the tissue, the flesh beneath the spot turns black and may extend to the center of the root. Tissue near the discolored area may have a bitter taste. Eventually, the entire root may rot. Roots that appear healthy at harvest can rot in storage, during transit, or at the market.