Silver scurf is a fungal blemish disease of potato tubers caused by Helminthosporium solani. The pathogen causes tan-to-gray circular lesions typically initiating on the stem-end of the tuber surface, often appearing shiny and silver when wet. Infection reduces both the visual appeal and quality of potato tubers, as the pathogen causes damage to the periderm or skin which enables the onset of other pathogens or enhanced desiccation. This disease is primarily a concern for stored, commercial fresh market potatoes.
Primary Source: Infested soil, debris-borne, infected seed potatoes, infected tubers in storage
Spread: Rain or irrigation washes spores through infested soil during initial spread. Once in storage, warm temperatures and high humidity allow sporulation to occur. Airborne spores can then infect new stored tubers.
Favorable Conditions: High humidity ( > 90%), high temperatures
The silver scurf disease cycle begins with primary infection, which can occur when overwintered spores (conidia) are washed through infested soil and plant debris and onto tubers. Other sources of primary inoculum are infected seed tubers, which can spread the pathogen to daughter tubers. The pathogen infects and causes lesions on the tuber, which can produce more conidia that are released into the soil. At the end of the growing season, H. solani conidia are able to overwinter in soil, and fungal parts can subsist in soilborne crop debris. Once harvested and in storage, the lesions on infected tubers can enlarge and again produce spores (sporulate) in moderate temperatures and high humidity. These spores can then spread and cause secondary infection in stored tubers.
Potato silver scurf disease cycle illustration
The following practices can help reduce inoculum and spread for this disease:
- Plant certified disease-free seed
- Rotate away from susceptible crops (2-3 years)
- Rogue volunteer plants
- Assess seed prior to planting, and daughter tubers prior to storage
- Disinfest storage spaces between uses
- Store at low temperature and humidity
- Avoid leaving potato tubers in the field for >2 weeks post vine kill
- Store potatoes in environments with good airflow and temperature control
Fungicides can be applied during the production season as well as post-harvest to limit silver scurf on potato. Up-to-date Wisconsin-specific conventional seed, in-furrow, and postharvest fungicide information and recommendations can be found in the Commercial Vegetable Production in Wisconsin (A3422), a guide available through the UW Extension Learning Store website. Or, for home garden fungicide recommendations, see Home Vegetable Garden Fungicides (D0062), a fact sheet available through the UW Plant Disease Diagnostic Clinic website. Always follow label directions carefully.
- Commercial Vegetable Production in Wisconsin (A3422) from the UW Extension Learning Store. This guide offers the latest recommendations for disease, insect, and weed management in Wisconsin’s most common commercial vegetable crops. Also included are lime and fertilizer recommendations as well as insect identification information and keys.
- UW Plant Disease Diagnostics Clinic. The University of Wisconsin-Madison/Extension Plant Disease Diagnostics Clinic (PDDC) provides assistance in identifying plant diseases and provides educational information on plant diseases and their control.
Written by Amanda Gevens, Ariana Abbrescia, Russell Groves, and Ben Bradford. Last updated Nov 2023