How to Manage Pests

Pests in Gardens and Landscapes

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.

Life cycle


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.

Pimple-like lesions of powdery scab
Pimple-like lesions of powdery scab

Statewide IPM Program, Agriculture and Natural Resources, University of California
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