| Abstract: | Control of rape diseases II. Measures for disease reduction caused by Sclerotinia sclerotiorum with consideration to economical aspects The most widely distributed diseases of rape in the Federal Republic of Germany are Sclerotinia sclerotiorum (white stalk disease, formerly called rape canker) and Phoma lingam (root collar and stalk rot), and these can cause considerable yield losses. S. sclerotiorum occurs sporadically and is more prevalent in the marsh land of northwest Germany than in the hilly landscape of Schleswig-Holstein, where pockets of infection are found. Application of calcium cyanamid, formerly successfully used to control apothecia formation by S. sclerotiorum, has been replaced by fungicides (Vinclozolin) directed at preventing ascospore infection. Many experiments proved to be economically unsuccessful due to the low rate of infection and the high costs involved with such treatments. With an expected yield of 30 dt/ha, an 8 % increase in yield following spraying must be achieved in order to make the fungicide treatment profitable. In fields where only up to 12% of the plants were infected, 75 % of the experiments proved to be uneconomical. By a disease index of 13–25 %, 55 % of the trials were similarly uneconomical. Only where more than 25 % of the plants were infected did the fungicide application prove to have a considerable effect on the yield. A prophylactic treatment is not to be recommended. Only in those areas where severe disease occurs nearly every year should such treatment be practiced that is unless the Advisory Service advises otherwise due to extreme weather conditions (too wet or too dry) which may lead to only very slight infection. |
