Black Dot

Small microsclerotia (overwintering structures) look like ‘black dots’ on the tuber surface, and are most easily seen with a microscope.

Causal Agent:

Colletotrichum coccodes


Pathogen of potato and relatives such as nightshades, tomato, and pepper. Overwinters in soil on plant debris or non-harvested tubers. Affected tubers occur consistently in some fields.


Seed tubers are commonly infected, and provide the most common way that black dot moves from field to field. Once soils are infested, they remain infested for some time.


  1. Avoid planting infected seed.
  2. Maintain good crop rotations of at least 3 years out of potato and other plants in the Solanaceae.
  3. Maintain good crop fertility and soil health.
  4. Promote good root health by not overwatering and avoiding soil compaction.

Further Reading:

Pacific Northwest Pest Management Handbooks

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