Blackleg

Blackleg (Pectobacterium carotovorum subsp. atrosepticum) attacks potatoes early in the season and is worst in heavy soils and rainy weather.

Symptoms
Tell-tale sign is the blackening of the stems at and below ground level. The leaves turn yellow and wilt; eventually the haulm withers.

Treatment
None. Lift and destroy affected plants.

Prevention
Never plant seed tubers that are soft and rotten. The practice of cutting seed tuber in half to make them go further increases the risk of attack.