Skin Spot
Polyscytalum pustulans
Pathogen
Fungus
Hosts
Potatoes
Symptoms
Tubers are covered by numerous raised spots surrounded by dark, sunken rings. Damaged eyes show no sign of growth.
Development
The initial sources of infection are seed tubers, which lead to a build-up of inoculum in the soil. Tubers are infected usually through injuries or the eyes during harvest, but the spots are not usually seen until December. Can survive for up to 4 years in the soil or for up to 8 years on plant debris.
Favourable Factors
Wet conditions at lifting and cold conditions early in storage. The use of sprout suppressants may increase the severity of the disease.
Importance
The appearance of infected tubers is spoilt and spots in the eyes can cause uneven emergence, blanking (rotting or failure of the seed tuber) or even crop failure.
Control
There are no known resistant varieties, but information on less susceptible varieties is available on the National List
Use disease free seed
Seed treatment fungicides can help to suppress inoculum
Lift early in warm, dry soil conditions
Clean and dis-infect stores where the disease has recently been encountered
Store tubers in dry conditions at 16-18C for a few days after lifting
Treating with fungicides and or fumigants within 2 weeks of lifting may reduce disease incidence
