Potato
Silver Scurf
Helminthosporium solani
Fungus
In a Nutshell
- Small silvery grey spots or lesions that enlarge into circles.
- They are usually irregular in shape and associated with the stolon end.
- Lesions usually remain superficial causing no damage to underlying tissues.
Can also be found in
Potato
Symptoms
Symptoms are normally present at harvest but the disease develops during storage. During storage, potatoes display silvery spots that enlarge into circles with defined brown margins. The lesions later coalesce and may turn brown, making them hardly visible on unwashed potatoes. The appearance of lesions also varies with the potato variety, mostly due to skin types. The outer skin layer of infected potatoes softens and wrinkles and eventually peel off. Secondary infections with other pathogens may occur.
Recommendations
Organic Control
Natural biocides (hydrogen peroxide) or biological products (Bacillus subtilis, clove oil) have shown limited or no efficacy in reducing the risk of infection with silver scurf.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. The application of fungicides to seed potatoes prior to planting or at harvest may prevent infection. Thiabendazole, applied to tubers as dusts, can reduce the incidence of silver scurf in the next season or during storage.
What caused it?
Silver Scurf is caused by the seed-borne fungus Helminthosporium solani. It survives on tubers for long periods of time and infects the skin. The infection can arise from the soil, the use of infected seed tubers or remaining spores in storage rooms. Temperatures of 3°C and relative humidities lower than 90% during storage hinders the development of the disease. The formation of condensation on the tubers during storage (warm air meets cold tubers) exacerbates the problem. Even though the potatoes are still edible, their market value is significantly reduced.
Preventive Measures
- Use seeds from healthy plants or from certified sources.
- Check for tolerant potato varieties.
- Implement wide crop rotation.
- Early lifting of tubers reduces the incidence.
- Control volunteer plants after harvest.
- Clean and disinfect tools and handling equipment between lots.
- Store potatoes in constantly cool and dry conditions, with good ventilation.
- Good sanitation and culling practices after harvest are essential.
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