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

Consortium Members and Partners


Insects, Diseases, Nematodes, & Beneficial Organisms

Find out more information about insects, diseases, nematodes, and beneficial organisms for Potatoes.

About The Northwest Potato Research Consortium

In February 2012 the state potato commissions in Washington, Idaho, and Oregon officially launched a new cooperative effort in research. The aim of this initiative is to increase cooperation and efficiency of the research programs funded by the three potato commissions that total about $1.5 million annually. It will also work toward comprehensive research results reporting process that aims to get useful information to the growers and industry members who need it. This website is a big part of that effort. Research results, integrated pest management guidance, and production information of many kinds will be presented here. For feedback or suggestions on this site, please contact Andy Jensen, Manager of the Consortium.

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A useful and resourceful research library available with a wealth of knowledge and insight into potato data from in field experience.

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