Gangrene – Phoma exigua var. foveata

Symptoms    Small dark lesions enlarge to form sunken, thumb-shaped marks anywhere on the tuber surface. Extensive, internal cavities develop lined with dark, almost black fungus. The boundary between diseased and healthy tissue is distinct.

Sources and Factors Favouring Development

Seed and soil-borne stems become infected via the seed.  Tuber infections result mainly from damage during harvesting.  Cold, wet conditions favour disease development.  The fungus can spread from infected tubers to adjacent ones during storage.

Control          Avoid the use of infected seed and highly susceptible cultivars. After harvest or grading, tubers should be kept at a temperature of 12-15°C for seven days to allow wound healing.  Ensure skins are fully set before harvesting and long periods low storage temperatures. Early treatment with an approved fungicide, can give effective control.