Although the most prevalent sweet potato diseases attack the roots, fungal leaf spots and lesions are common but rarely cause economic losses.
On tubers, silver scurf is rather prevalent. On the surface of diseased tubers that have been stored under high humidity, a fine covering of dark green to black spores, visible only in mass to the human eye, can sometimes be detected.
Air space, which occurs from fungus growth beneath the tuber periderm, causes these patches, which can cover a substantial percentage of the tuber.
On some white–skinned cultivars, symptoms are difficult to identify, but on those with red skin, they are clear.
Ring rot is caused by Pythium spp., a common soil-borne fungus that also parasitizes many other plants, hence sweet potato must be rotated.
Sunken, chocolate-colored lesions appear on infected roots and tend to spread laterally forming a ring around the sweet potato is common.
The soft decay has spread to the interior of the building. Losses are most common late in the season, when the weather is chilly and rainy.
Rhizopus and bacterial soft rots and souring can cause similar symptoms. In most cases, ring rot does not spread in storage. Harvest prior to cool, wet seasons to manage this disease.
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