Black rot

The disease is caused by the fungus Ceratocystis fimbriata. Dark circular spots appear on infected roots. These spots can expand to cover much of the sweet potato. Small black fungal fruiting bodies (perithecia) develop and are visible at the centre of the spots. The diseased tissue is darkened and bitter in taste. On young sprouts black spots develop eventually encircling the plant causing dwarfing, yellowing of the foliage and finally death.

The fungus survives in the soil in diseased plant debris and also in diseased stored roots. The disease is favoured by temperatures near 25⁰C and moist soil conditions. In storage, decay progresses most rapidly in moist conditions at temperatures of 14 to 27⁰C.