Blackleg – Erwinia carotovora subsp. atroseptica (Eca), bacteria
The pathogen can survive in soil as well as seed; however, planting infected seed pieces into wet, cold soils under anaerobic conditions results in the most severe losses in stand and yield. The bacteria enter the tubers through stolons during the growing season, with black sunken lesions resulting at the stem end. Infection normally spreads from the stem ends through the heart of the tuber. Internally the infected tuber flesh first appears cream colored, then turns grayish and black with a mushy texture like bacterial soft rot. Typically, infected tubers have soft rot only in the pith region, but in an advanced stage secondary soft rot bacteria may predominate (Ecc and Echr) and confuse the diagnosis. Control in the field relies upon disease–free seed that is adequately warmed and sprouted, and planted in soil with a minimum temperature of 50° F at a 5–6–inch depth. Rotations of 2–3 years between potato crops may also help.