Epidemiology, forecasting and management of winter oilseed rape diseases in the UK

Survey results show that the most serious diseases on winter oilseed rape in the UK are light leaf spot (Pyrenopeziza brassicae) and stem canker (Leptosphaeria maculans), then stem rot (Sclerotinia sclerotiorum) and dark pod spot (Alternaria brassicae); severity of epidemics differs between seasons, between regions and between crops. Diseases cause losses of up to £80M each season, despite expenditure of up to £12M on fungicides to control them. Light leaf spot is a polycyclic disease initiated in autumn (GS 1,05), probably by wind-borne ascospores, and spread by splash-dispersed conidia. Stem canker is a monocyclic disease; in autumn wind-borne ascospores infect leaves to cause phoma leaf spots and the pathogen grows down petioles to stems, on which canker lesions are observed in spring (GS 6,4). Regional forecasts predict risk of severe light leaf spot epidemics and can be modified by specific factors (e.g. cultivar, sowing date) to estimate risks in individual crops. A protocol for confirming the presence of light leaf spot involves sampling crops, incubating plants and assessing the appearance of diagnostic white pustules of the pathogen. Field experiments have suggested that growers need to consider control of light leaf spot and stem canker in autumn and late winter and control of stem rot and dark pod spot in spring