Pythium Leak

Occurs wherever potatoes are grown. This pathogen only enters through wounds. There is usually a distinct line between healthy and diseased tissue. Infected tissue is a smoky grey color. When squeezed, infected tubers produce a dark watery liquid. Followi

Causal Agent:

Pythium ultimum and sometimes other Pythium species.


Wide host range including many crops. Infection of tubers occurs at wounds.


Infection can spread from tuber to tuber during harvest and handling. Infected seed can also spread the pathogen.

Fungicide Resistance:

Pythium has begun to demonstrate resistance to fungicides.


  1. Crop rotation and destruction of diseased tubers are important.
  2. Some fungicides applied at planting or during the growing season can reduce losses caused by Pythium leak.
  3. Harvest with pulp temperatures between 45 and 65 degrees F.
  4. Minimize mechanical injury to tubers during harvest and handling.
  5. In storage, encourage maximum suberization and wound periderm formation; do not allow free water on tubers.

Further Reading:

Pacific Northwest Pest Management Handbooks

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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 Raina Spence, Manager of the Consortium.

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