Sweet Potato Scurf

Sweet potatoes can be grown in large containers and they look lovely on a patio.


And sometimes they get sick with a fungal disease called sweet potato scurf.

Purple sweet potatoes growing in a large container (Kate Russell)

The lush aboveground growth of your sweet potato plant may give no sign of sickness, at first. If you were to dig up a portion of the root system, however, you would see discolored areas of various sizes and shapes. These superficial lesions tend to be gray on yellow-fleshed sweet potatoes and purple, brown, or black on orange-fleshed varieties. These discolorations look similar to black scurf and silver scurf of regular potatoes. Unlike silver scurf, sweet potato scurf does not penetrate beyond the skin. Eventually, these lesions can be seen on the stems and leaves of heavily infected plants.


While sweet potato scurf (or soil stain) doesn’t look too terrible and can be scraped off, these fungal infections make it more likely that other diseases and pests will get in. Held in storage, infected sweet potatoes dry out faster.


Conducive conditions

Humidity is necessary for sweet potato scurf to develop. It often appears during the rainy season. And it is more likely to occur in areas with heavy soil and in areas that have been top dressed with a lot of manure, or that contain high levels of organic matter. Normally, organic matter helps plants grow better. Apparently, sweet potatoes stay healthier when grown in light, sandy soils.

Sweet potato infected with scurf (Scot Nelson) Public Domain.jpg

Sweet potato scurf management

Sweet potato scurf is caused by the Monilochaetes infuscans fungi. This isn’t a particularly resilient  fungus. Without a host, it generally only survives for 1–3 years in the soil, depending on the soil type. This makes crop rotation a very effective control. In areas where sweet potato scurf has been a problem, growers generally use a 3- or 4-year rotation.


Spores can be spread via tools, clothing, baskets, and shoes, but mostly through infected plant material. This means you can often avoid it by only planting certified disease-free slips. Slips are baby sweet potato vine cuttings used to make new plants. Commercial growers treat slips with fungicide before planting, but there are no fungicides that can be used to control the disease once it takes hold.