Powdery scab

Powdery scab, is a disease that occurs in potato tubers, caused by the protozoa Spongospora subterranea.

Symptoms
Symptoms 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. The powdery pustules contain resting spores, which release anisokont zoospores which can infect the root hairs of potatoes or tomatoes.