Kansas State University | College of Agriculture | Department of Plant Pathology | Site Map | Home

Black rot, caused by the fungus Ceratocystis fimbriata, is a highly destructive disease of the sweet potato. The fungus attacks all underground parts of the plant and causes decay of the fleshy roots in both field and storage.

The black rot fungus causes somewhat circular, metallic-black, dry and corky decayed areas on the surfaces of affected roots in both field and storage. This fungus causes localized lesions, being different from the stem rot fungus which invades and spreads widely within the tissues of stems, crowns, and roots,

but causes no external lesions. In black rot, the size of the metallic-black lesions may vary from small spots to large infected areas. Black rot usually does not cause affected roots to decay completely.

As the black rot fungus invades sprouts in the hotbed, it penetrates all tissues and kills the young stems. The blackened, infected sprouts may be killed before they emerge through the hotbed soil. Above-ground symptoms are not always noticeable, although leaves of severely affected sprouts usually have a sickly, yellow appearance.

DISEASE CYCLE

The fungus overwinters in affected tissues of stored roots, in field soil. The fungus usually infects plants through wounds, although it may penetrate the host directly.

CONTROL

Sanitation is very important for the control of black rot. Plant only certified, disease-free roots or slips. All hotbeds should be disinfected with steam, methyl bromide, vapam, chloropicrin, or some other type of fumigant before planting. Slips should receive a fungicide dip prior to planting. The fungicide thiabendazole (Mertect 340-F) is labeled for several diseases of sweet potato as a preplant dip. Seed roots should be treated for 1-2 minutes, then planted. Cultural practices in the field, including weed control, insect management, and sweet potatoes at harvest should be done with care to avoid bruises and mechanical injuries. Storage facilities should be thoroughly cleaned before harvest.

Web updated 9/01/06
Web comments to jpierz@ksu.edu