Powdery scab, caused by the protist Spongospora subterranea, is widespread in potato growing countries. Symptoms of powdery scab include small lesions in the early stages of the disease, progressing to raised pustules containing a powdery mass. Powdery scab has a cosmetic effect on tubers, which can result in rejection of potatoes.
- University of Maine. "Powdery Scab of Potatoes".
- The Royal Horticultural Society. "Powdery scab of potatoes (Spongospora subterranea f. sp. subterranea)". Retrieved 2007-05-06.
- Cornell University. "Powdery scab photos".
- "Resistance to Powdery Scab in Potato" (PDF). US Department of Agriculture.