Blackleg

Blackleg is caused by Erwinia carotovora var atroseptica and is found in all potato production areas. It often occurs in conjunction with soft rot bacteria and under suitable conditions will cause heavy losses.

Disease symptoms include missing hills and plant yellowing at flowering when one or more stems on a plant may suddenly wilt and die. The lower part of the stem is black in colour, extending from just above the soil line to about 15 cm up the stem. These "blacklegs" occur with varying degrees of intensity in a crop but are most frequent, when present, in low areas of the field. Stem-end tuber rot can cause problems in storage. Blackleg is spread in or on seed tubers. The pathogen does not survive in soil for more than a year in the absence of a host. Moist soil and cool temperatures favour the spread of this pathogen in the potato crop.

Control

Planting whole seed that is free of blackleg and other diseases provides effective control. Plant in well drained soil and avoid excessive irrigation. Treat cut seed tubers with recommended fungicides and plant immediately or suberize cut seed well before planting to reduce infection by Fusarium spp. and other pathogens that predispose the tuber to bacterial invasion. Plant on land with at least two or three years rotation between potato crops. Remove potato cull piles and infected volunteer plants to eliminate sources of bacteria which can be transmitted by potato infesting insects. Frequently clean and disinfect seed cutting and handling equipment as well as planters, harvesters and conveyers to eliminate contamination. Avoid washing seed potatoes unless absolutely necessary, and exercise care during handling operations to minimize damage. Seed growers should remove infected plants as soon as they appear. Russet Burbank is intermediate in resistance. All other cultivars are susceptible.