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.
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.
No biological control strategies have been developed for Pythium leak.
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.
Fungicide applications applied in-furrow at planting or to foliage during early tuberization can reduce tuber infection at harvest. Resistance to mefenoxam has been reported in several Pythium species.
Common/Trade Name |
Product per Acre |
Application Frequency
|
Remarks |
Mefenoxam Mixtures |
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|
Ridomil Gold Bravo |
2 lb |
14 days |
Maximum of 3 applications, alternating with a full rate of a protectant fungicide; 14 day PHI |
|
Ridomil Gold MZ |
2.5 lb |
14 days |
Maximum of 3 applications, alternating with a full rate of a protectant fungicide; 14 day PHI |
|
Ridomil Gold Bravo Liquid |
1 pack per 10 acres |
14 days |
Maximum of 3 applications, alternating with a full rate of a protectant fungicide; 14 day PHI |
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Potato, Disease, Pythium Leak
Date: 03/29/05