Pathogen. The fungus persists mainly in infected potato tubers.
Disease development. Skin spot is favoured by low temperatures and high humidity. During the season, spores produced on infected seed tubers infect below- ground plant parts. The fungus infects the daughter tubers through lenticels, eyes and wounds.
Symptoms. The symptoms on tubers are easier to see after the potatoes have been in storage for a few weeks. Skin spot can spread in storage.