Skin Spot Potato Disease

Skin spot (Polyscytalum pustulans) is a fungal pathogen of potatoes which is normally invisible until after around two months of storage, when areas of infected tissue begins to show spots.

Common Signs and Symptoms of Skin Spot

The main symptom of skin spot is the appearance of slightly raised spots, blue to black in colour, on the surface of infected tubers, which develops gradually during storage.

Symptoms are also present in both the eye (killing off of bud tissue), sprout (blackening and withering) and root (orange/brown discolouring of outer layers).

Common Causes and Conditions of Skin Spot

Skin spot is encouraged by wet conditions when lifted, and further encouraged when stored in cold conditions.

Immune / Vulnerable Varieties

There are no potato varieties which are particularly vulnerable or resistant to skin spot.

Controlling Skin Spot

Cultural and Methods:
Sprouting seed early and discarding any infected tubers.

Curing your crops for a few days at between 16 – 18 degrees after lifting, and ensure storage conditions are kept dry can also help control skin spot.


If applied within two weeks of lifting, thiabendazole, imazalil and fumigant 2-aminobutane, may help to reduce incidences of skin spot.