Silver scurf

Silver scurf (Helminthosporium solani) is a fungal disease of potatoes that causes blemishes on the surface of the tubers. The longer tubers remain in the soil, the more severe the problem can become. It is encouraged by humid, warm conditions. Silver scurf may be confused with black dot, which can sometimes appear silvery, they are distinguishable when compared side-by-side.

Symptoms
The first signs are silver-grey spots on the surface of tubers, which may enlarge into darker-margined circles. Eventually they may cover very large areas of the skin, which are then begin to shrivel as the scurf causes water loss.

Treatment
Thiabendazole applied within two weeks of lifting may reduce incidence if it has not been used previously on the seed. Thiabendazole and imazalil may also be effective as seed treatments to protect progeny crops. Many populations of silver scurf are now exhibiting insensitivity to thiabendazole.

Prevention
No resistant varieties are available. Harvest early and store in cool, dry conditions.