Development of a system for forecasting severe light leaf spot in winter oilseed rape

In the UK, an estimated £3-9 M are spent each year on fungicides to control winter oilseed rape diseases, but losses in excess of £30 M still occur [1]. Light leaf spot (Pyrenopeziza brassicae) is one of the major diseases of winter oilseed rape. The optimum time for control of severe light leaf spot is in the autumn [2], but symptoms often do not appear until later (December-February). Disease epidemics differ in intensity between seasons and between regions. However, many growers make spray decisions on the basis of local practice rather than on the actual disease levels present. Consequently, many crops with severe light leaf spot epidemics are left unsprayed whereas crops with little disease receive a full fungicide programme. Growers require a more accurate method to determine the need for fungicide sprays. Work on a forecasting system, being developed to predict severe light leaf spot epidemics and associated field experiments, is reported