Improving strategies to control stem canker in the UK

The fungicides difenoconazole, flusilazole + carbendazim, prochloraz + carbendazim and tebuconazole applied as two or four spray treatments at full or half dose gave good control of phoma leaf spot on canker-susceptible winter oilseed rape cv. Rocket. Treatments were applied when 100% plants had phoma leaf spot and only four sprays of difenoconazole or flusilazole + carbendazim at full or half dose gave good (>65%) control of canker. These fungicides appear to limited curative activity and two spray treatments equivalent to commercial practice gave poor control. Monitoring of crops on farms suggested that an increase in the use of autumn fungicides from 34% crops in 1995 to 64% in 1998 together with better spray timing is improving canker control. Further work is needed to predict the onset of the autumn leaf spotting which is very variable and to optimise use of fungicides