Powdery scab—Spongospora subterranea
The powdery scab pathogen infects lenticels and wounds in tuber surfaces. Tuber cells are stimulated
to divide and enlarge, causing the formation of small, purplish brown, raised lesions. The pimple-like
lesions or pustules are about 0.13 - 0.25 inch in diameter. They gradually darken and decay, leaving shallow
depressions filled with powdery masses of dark brown spore balls. Roots may also be infected, resulting
in the formation of small, white galls that also break down to release masses of spore balls.
Powdery scab can be minimized by using good cultural practices. Use pathogen-free
seed tubers, do not
use manure from farm animals that have fed on infected tubers, and avoid moving soil from contaminated
fields to uninfested areas.
lesions of powdery scab