HPIPM:Potato Pythium Leak

Author: Howard F. Schwartz and David H. Gent

Identification and Life Cycle

Leak is caused by several species of the fungus-like organism Pythium, but P. ultimum var. ultimum appears to be most important in the High Plains. P. ultimum is a very common soilborne pathogen, and can attack many or most crops. Disease begins when P. ultimum enters tubers through wounds made during planting, harvest, and handling operations. Disease is most severe when temperatures are high (77 to 86ºF), but disease generally does not develop below 50ºF. The pathogen produces thick-walled structures called oospores that remain viable in soil for years. P. ultimum may survive between potato crops as dormant oospores, pathogenically on weeds and other crops, or may be introduced into fields in irrigation water.

Plant Response and Damage

Leak symptoms begin as light tan water-soaked lesions around wounds on the periderm. Tissues swell around the wound, and the periderm becomes discolored and moist. A dark, distinct boundary between healthy and diseased tissue is apparent in infected tubers. Diseased tissues become watery and may contain cavities. When infected tubers are squeezed, dark, watery ooze is produced. When infected tissues are cut open the affected areas changes to a gray-brown to black color, and may have a pink tinge. In storage, tubers may totally rot within a week, leaving only tuber shells with thin skins. Yield losses can be significant, and are directly related to tuber bruising and injury.

Biological Control

No biological control strategies have been developed for Pythium leak.

Cultural Control

Crop rotation provides some disease suppression, but does not eliminate the leak pathogen from fields. Delay harvest at least 14 days after vine killing to promote skin set to reduce tuber susceptibility to injury during harvest and storing operations. Avoid harvesting tubers above 70ºF. Promote rapid wound healing before long term storage of tubers. If leak develops in storage, increase air movement, and cool and dry the crop as quickly as possible.

Chemical Control

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.