Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Potato (Solanum tuberosum) -- Powdery Scab
 
Cause: A fungus, Spongospora subterranea, that is carried on seed and can survive 3 to 10 years as cysts in soil.
Symptoms: Purple to brown raised lesions on the tuber surface. It usually is evident that the potato's epidermis has broken away to expose the powdery mass of cysts. Small galls and warts form on the roots of some potatoes and other plants in the potato family.

Notice the scabby areas on the surface of the tuber, characteristic of powdery scab.

Scabby, warty lesions on a tuber infected with powdery scab.

Lesions are filled with dark-brown spore balls (bottom left) that contain numerous resting spores (above).

 
Cultural control:

  1. Avoid planting contaminated seed.
  2. Avoid planting on ground known to be contaminated.
  3. Rotate out of potatoes for 3 or more years if replanting cannot be avoided.
  4. Do not move contaminated soil to clean fields on field machinery, shovels, or boots.
  5. Reduce irrigation; excessive irrigation favors the disease.
  6. There is less damage to 'Russet' cultivars than to white or red cultivars.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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