Disease in Potato :Phoma Rot or Pocket Rot

Scientific Name

• Phoma exigua var. exigua

Identification

• Tubers become infected through wounds caused by rough handling during harvest and grading operations, leading to the development of the disease in storage.
• External lesions are circular, slightly sunken, greyish-brown, and the size of a thumbprint. The tissue underneath the lesions is black, shrunken, and decayed, with cracks often forming on the surface of the lesions.
• The black, rotten tissue can be easily scooped out from the surrounding healthy tissue.

Often Confused With

• Fusarium dry rot

Biology

• The fungus persists either in the soil or on infected seed tubers.
• Infection occurs through wounds or bruises at harvest or when grading. Disease incidence is higher when the soils are wet and cool at harvest.

Period of Activity

• Infection occurs at harvest, and the disease develops in storage.

Scouting Notes

• There are no above-ground symptoms.

Thresholds

• No established thresholds.

Management Notes

• Use healthy, certified seed.
• Minimize tuber wounding and/or bruising at harvest and during potato grading operations.