Symptoms
Brown to greyish-black blotches on the skin of the storage root that stay superficial and do not enter the flesh. Affected roots look unsightly, lose moisture faster and store poorly.
Prevention
Plant disease-free slips from clean nurseries and rotate away from sweet potato for two to three seasons. Cure and store roots in a dry, well-ventilated place.
Treatment
Organic
Select only clean roots for planting material and dip slips in a Trichoderma suspension before planting. Discard scurfy roots rather than using them as seed.
Chemical (last resort)
Treat planting material with a thiophanate-methyl or mancozeb dip before planting. The disease is cosmetic and rarely warrants field spraying — observe PHI.
Affects 1 crop
Sources
MARDI Sweet Potato Production Guide; DOA IPM Manual