Polyscytalum pustulans

(Skin spot)

• Causal agent and transmission

Skin spot is caused by the fungus Polyscytalum (formerly Oospora pustulans) encountered in cold and damp regions of potato cultivation, such as Great Britain and Scandinavia, where heavy soils are prevalent.

The infection can come from the soil or from the seed tuber. The disease may survive for several years in the soil in the form of sclerotia.

• Significance

Skin spot is a minor disease of potato tubers. However, in heavy and cold soils, such as in northern European countries, it can have an economic impact for the ware potato industry, when tubers are washed before selling.