10/05/2011 image expired

The lack of adequate rain throughout much of Britain has resulted in unseasonably dry ground in a large part of England and Wales. These conditions carry with them the risk of higher levels of common scab than in previous years.

Chris Steele, technical executive for The Potato Council, warned growers not to underestimate the threat posed by scab; "The disease costs the industry about £4m a year in rejections and remains quite a problem. It mostly affects the fresh sector that depends more on the cosmetic appearance of tubers. Most supermarkets draw the line at 5 per cent infection."

Infection is most likely to occur for six weeks after the start of tuber initiation where soils are dry, when Streptomyces scabiei, the causal agent, multiplies significantly on and around developing tubers. As tubers grow, the lesions enlarge and infected areas of the potato respond, producing a corky layer, eventually producing rough, brown mature scab lesions.

Steele also extolled the value of good irrigation; "Irrigation is an important method of control that should be considered part of a management programme starting much earlier.” However, he also explained the necessity of careful management of an irrigation programme, saying, “Do not do half a job – work has shown ceasing irrigation after two weeks still allows scab to infect tubers, and could actually exacerbate disease levels.”