Blackleg is caused by several species of bacteria in the genus Erwinia, namely E. carotovora subsp. carotovora, E. carotovora subsp. atroseptica, and E. chrysanthemi. These bacteria can be carried in and on seed tubers, primarily in lenticels and wounds, and are spread among seed pieces during cutting, handling, and planting. When planted, the bacteria begin to rot seed pieces. The bacteria may totally rot seed before emergence, or a sprout may emerge and bacteria may move upward in water conducting tissues and cause blackleg. Bacteria can be washed from infected seed pieces and carried in soil water to daughter tubers, where they infect them through lenticels and wounds. Movement of bacteria through stolons from diseased plants also may infect daughter tubers. Disease is most severe when warm temperatures follow planting of contaminated seed pieces in cool, wet soils. Erwinia spp. that cause blackleg survive between potato crops in and on tubers, crop debris, irrigation water, and pathogenically on other hosts.
Blackleg symptoms may occur at any stage of plant development. As bacteria move upward on stems, small water-soaked lesions become apparent at the base of stems. Lesions can expand and extend into the upper plant canopy. Affected tissue is soft under humid conditions, but becomes shriveled under dry conditions. Vascular tissues are generally a light brown to black color above areas of visible blackleg symptoms. Plants are stunted, and have wilted, chlorotic foliage.
No biological control practices have been developed for blackleg.
Plant well-suberized seed pieces in warm, well-drained soils. Avoid irrigation before emergence, which can greatly increase seed piece decay and blackleg development. Adjust harvest and handling-equipment to minimize tuber bruising and injury. If possible, avoid harvesting when soil temperatures are greater than 68 to 77ºF. Cover trucks to prevent tuber heating during transport. In storage, promote rapid wound healing with 95% relative humidity and temperatures of 50 to 55ºF for 10 to 14 days. Tubers should be stored at less than 50ºF with adequate aeration after wound healing.
Trade Name |
Rate |
Remarks |
Streptomycin |
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Seed Treatment for Potatoes LD |
1 lb per 100 lb of seed |
Apply for thorough coverage to whole or cut seed. |
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Agri-mycin 17 |
100 ppm (4 oz per 100 gal of water) |
Soak cut seed pieces in streptomycin solution for several minutes. |
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, Blackleg
Date: 03/29/05