Answer: You're sweet potatoes have scurf a fungal skin infection, says Phil Dukes, plant pathologist specializing in sweet potatoes at the U.S. Vegetable Laboratory in Charleston, South Carolina. The fungus attacks only sweet potatoes, causing the skin to turn black. It doesn't affect the plant health or flavor, but can shorten the storage life of the tuber. Growing sweet potatoes in well drained soil with a pH of 5.5 and rotating crops--not planting sweet potatoes in infected soil for three years--helps control the disease. Also avoid applying manures, since they can carry the fungus, and don't take cuttings for next year's slips from infected tubers, suggests Dukes.
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