Potato (Solanum tuberosum)-Powdery Scab

Cause A soilborne organism belonging to the cercozoan group, Spongospora subterranea, that is carried on seed and can survive 3 to 10 years as cysts in soil. This microorganism also transmits Potato Mop Top virus.

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. Similar to symptoms caused by common scab.

Cultural control

  • Avoid planting contaminated seed.
  • Avoid planting on ground known to be contaminated.
  • Rotate out of potatoes for 3 or more years if replanting cannot be avoided.
  • Do not move contaminated soil to clean fields on field machinery, shovels, or boots.
  • Reduce irrigation; excessive irrigation favors the disease.
  • There is less damage to 'Russet' varieties than to smooth-skin varieties.

Chemical control

  • Omega 500F at 1.5 to 3 pints/A banded in-furrow for disease suppression. Do not apply within 14 days of harvest. 12-hr reentry.