Skin Spot
Beginner
Scientific Name
Polyscytalum pustulans
Identification
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.
Initial symptoms are pimple-like spots on the tuber surface. The spots may be up to 2 mm in diameter and are either distributed at random over the tuber surface or concentrated around the eyes or stem end. The pimple-like spots are darker than the healthy areas. When wet, they appear purplish-black.
The lesions may grow together to form larger diseased areas.
Often Confused With
N/A
Period of Activity
Activity of the fungus is favoured by low temperatures and high humidity.
Scouting Notes
There are no above-ground symptoms.
Thresholds
No thresholds are established. Not a common disease in Ontario.
Advanced
Scientific Name
Polyscytalum pustulans
Identification
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.
Initial symptoms are pimple-like spots on the tuber surface. The spots may be up to 2 mm in diameter and are either distributed at random over the tuber surface or concentrated around the eyes or stem end. The pimple-like spots are darker than the healthy areas. When wet, they appear purplish-black.
The lesions may grow together to form larger diseased areas.
Often Confused With
N/A
Biology
The fungus persists mainly in infected potato tubers.
Skin spot is favoured by low temperatures and high humidity. During the season, spores produced on infected seed tubers infect belowground plant parts. The fungus infects the daughter tubers through lenticels, eyes and wounds.
Period of Activity
Activity of the fungus is favoured by low temperatures and high humidity.
Scouting Notes
There are no above-ground symptoms.
Thresholds
No thresholds are established. Not a common disease in Ontario.
Management Notes
- Plant healthy, certified seed.
- Minimize tuber wounding and/or bruising at harvest and during potato grading operations.
