The disease costs the industry £4m a year in rejections and mainly affects the fresh sector, which more heavily depends on tubers' cosmetic appearance.
Most supermarkets draw the line at five per cent infection and, although the processing sector is more tolerant, pitted lesions can cause problems because the potatoes are likely to be rejected if they have to be peeled more than four times.
Infection is most likely to occur for six weeks after the start of tuber initiation where soils are dry, when causal agent Streptomyces scabiei multiplies significantly on and around developing tubers.
As the tubers grow, the lesions enlarge and infected areas of the potato respond, producing a corky layer and eventually producing rough, brown, mature scab lesions.
Potato growers can request copies of Managing the Risk of Common Scab, produced by the Potato Council, by emailing Chris Steele at firstname.lastname@example.org or by calling 02476 478779.