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Soft rot of sweet potatoes, caused by the fungus Rhizopus spp., a common disease of the fleshy root in storage, is the most prevalent and destructive of the diseases that affect stored sweet potatoes. The root also may become infected in the hotbed and soft rot occasionally may destroy sweet potatoes in the field. Infections occur through wounds. After the fungus enters the tissues, it penetrates rapidly and causes a soft wet decay of the entire root in a very few days. Ring rot is a type of soft rot in which infection is not present at the root ends and decay develops in a ring around the sweet potato. The decayed tissues become dry and both ends of the root remain sound. A combination of wet soil and low temperature at harvest time causes sweet potatoes to be especially susceptible to soft rot. Rotting frequently appears soon after the roots are stored, particularly when temperatures are kept too low during the early part of the storage period when roots still have unhealed wounds. The disease may continue to develop throughout the storage period when suitable conditions, including low temperatures and high humidities, prevail and when fresh wounds are present. CONTROLBecause soft rot infections occur through wounds, it is important to avoid injuring sweet potatoes. It is particularly important to avoid injuring cured sweet potatoes as they are being taken from storage to be marketed. Cured sweet potatoes are more susceptible to soft rot than they were at harvest time. High curing temperatures can be provided to prevent decay from harvesting wounds but such decay-preventive environment cannot be provided during the time sweet potatoes are being marketed. Sweet potatoes should be placed in a warm, humid environment to cure as soon as they are harvested so their wounds can heal rapidly. After the roots are cured, they should be left undisturbed until they are marketed.The fungicide Botran is labeled as a postharvest control for soft rot. The fungicide may be applied as a spray during lifting operations or as a prestorage dip of the roots.
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This section was taken from Kansas State Experiment Station Bulletin 495.
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Web updated 9/01/06 |