Le plant français de pomme de terre FNPPPT Semae

Skin Spot

Polyscytalum pustulans

Causative agent and transmission

Skin spot is caused by a Polyscytalum (formerly Oospora) pustulans fungus encountered in cold and damp regions of potato cultivation, such as Great Britain or Scandinavia, particularly in heavy soil.

The infection can come from the soil or the seed potato.

Description of symptoms

(clic on photos to enlarge)

• On tubers: small dark blisters 0.5 to 4 mm in diameter developing on the surface of the tubers, either isolated, or in groups around the eyes and particularly the stem-base.
These protruding and conical blisters are generally surrounded by a depressed ring. The underlying tissue is corky and detaches rapidly.

The symptoms can develop during the first weeks of storage if drying is insufficient.

• On the roots, stolons and sprouts: superficial and cracked brown lesions, resembling those in black scurf.

The disease often remains unnoticed except when there are substantial attacks around the eyes that prevent germination.


  • Use of healthy seed potatoes;
  • Crop rotation;
  • Early harvesting and thorough drying.

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