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Ministry of Agriculture, Food and Rural Affairs

Phoma Rot, Pocket Rot

External and internal phoma rot symptoms Severe Phoma symptoms
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Beginner

Scientific Name
Phoma exigua var. exigua

Identification
Tubers are infected through wounds caused by rough handling during harvest and grading operations. The disease develops in storage.

External lesions are circular, slightly sunken, greyish-brown and the size of a thumb print. Underneath the lesions, the tissue is black, shrunken and decayed. Often cracks form 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

Period of Activity
Infection occurs at harvest. The disease develops in storage.

Scouting Notes
There are no above-ground symptoms.

Advanced

Scientific Name
Phoma exigua var. exigua

Identification
Tubers are infected through wounds caused by rough handling during harvest and grading operations. The disease develops in storage.

External lesions are circular, slightly sunken, greyish-brown and the size of a thumb print. Underneath the lesions, the tissue is black, shrunken and decayed. Often cracks form 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 takes place 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. The disease develops in storage.

Scouting Notes
There are no above-ground symptoms.

Thresholds
No thresholds are established.

Management Notes

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