Pathogen

Bacterium

Hosts

Potatoes

Symptoms

Stems fail to emerge or are stunted with yellow curled up leaves. These stems can be easily pulled out and are blackened at ground level. A late attack may cause the collapse and blackening of the entire haulm.

Development

The disease is primarily carried on seed tubers. Bacteria released from the rotting seed tuber attack developing shoots and prevent emergence. Later attacks cause a wet rot on emerged stems (blackleg). The disease also develops in daughter tubers as soft rot.

Favourable Factors

Wet conditions

Importance

A few infected plants may be found in most crops, but losses in the growing crop are usually small.

Control

• There are no resistant varieties, but information on less susceptible varieties is available on the National List.

• Avoid planting or cutting infected seed tubers.

• Avoid lifting under wet conditions

• There is no satisfactory chemical treatment.

Blackleg on potato stem (© Blackthorn Arable)