What you see: Dark patches on the skin of your sweet potato
What it is: Scurf, a sweet potato fungus
Eat or toss? Peel and eat! This fungus only grows on the surface of the potato, so once you’ve peeled it, you’ve eliminated the problem
Sweet potatoes looking a bit spotty? They may have something called “scurf.” This fungus manifests as dark brown to grayish patches on the skin of the sweet potato. It can look rather shadowy and foreboding, but there’s nothing to fear here. Simply peel the potato and, as long as everything looks normal beneath the skin, you’ve peeled off the problem.
But, once you spot some scurf, try to use up the sweet potatoes quickly. There are a couple of reasons for this, according to Brandon Parker, an agriculture agent with North Carolina State University's cooperative extension program. First, scurf-infected sweet potatoes could pass their condition along to other sweet potatoes. Second, even though scurf is only skin deep, if the sweet potatoes are stored for an extended period of time, say, several months, they could be more susceptible to other, less friendly invaders. Such pathogens could cause rots that will make the potatoes unusable.
Brandon Parker - Extension Agent, Agriculture - Commercial Horticulture - Johnston County Center - North Carolina State University Cooperative Extension
Penn State Extension - Scurf on Sweet Potato
Plant Pathology Extension - North Carolina State University - Sweetpotato Scurf
North Carolina Sweet Potato Commission - Diseases & Disorders
Scurffy, but lovable!