Common Scab

Typical raised scab lesions.

Causal Agent:

Common scab is caused by several species of Streptomyces, a genus of bacteria that is present in all soils in huge numbers.


Most soils contain bacteria capable of causing potato scab, but exactly what conditions bring on symptoms is not fully understood. Scab-causing bacteria are constantly changing the arrangement of genes in their DNA, which may explain some inconsistency in field management.


  1. Reliable strategies are not known for scab prevention under all conditions.
  2. Avoid planting scabby seed tubers.
  3. Plant varieties with scab resistance when possible.
  4. Avoid application of soil amendments that increase soil pH.
  5. A generally healthy crop may help reduce scab intensity on tubers.

Further Reading:

Pacific Northwest Pest Management Handbooks

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