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Disease Management
Pre-planting
There was a time when almost all potato tubers were contaminated with the blackleg bacterium. That is no longer true today. The use of healthy tissue culture plantlets to initiate seed potato stocks has broken the cycle of carrying tuber contamination forward from year to year. Also by limiting the number of field generations to 5 to 7 years for production of individual seed lots after tissue culture, the buildup of tuber contamination is curtailed. Hence the incidence of blackleg is significantly lower than it was before the incorporation of tissue culture into seed potato production programs. Although disease reduction has been very significant in some geographic areas, the disease remains important in others where similar practices are used. The reason for the difference in disease incidence is unclear but is probably related to the rapidity by which new seed stocks are exposed to blackleg inoculum. The risk of exposing new seed stocks to inoculum will depend on specific agronomic practices and the ability of the bacterium to persist outside of potatoes in the prevailing climatic conditions of the different geographic locations.
At planting
Planting limited generation seed in well-drained soil after soil temperature has increased above 10°C/50° F is recommended for avoiding the development of blackleg.
During the growing season
Roguing out blackleg-diseased plants including belowground portions reduces soil inoculum but is only a useful practice if precautionary measures are taken to prevent contact of diseased tissue with other plants in the field.
At harvest and during storage
Avoiding injury to potato tubers during harvest is important to minimize decay in storage. Removal of decayed potatoes before they spread their contents over grading lines and bin pilers avoids spreading the bacterium to other tubers. Wound healing is important in the early phase of potato storage to prevent development and spread of rots. During storage, however, the potatoes should be kept at a low temperature with adequate aeration to provide a dry environment and to prevent condensation of moisture on tuber surfaces.