Weed control in winter oilseed rape - evaluation of herbicide trials from 1971-1988
1990
Wahmhoff, W. (Goettingen Univ. (Germany). Forschungs- und Studienzentrum Landwirtschaft und Umwelt)
249 herbicide trials with 1851 treatments carried out between 1971 and 1988, were evaluated to determine the efficacy and cost effectiveness of various herbicide treatments in winter oilseed rape. Compared to cereals, a larger variation was observed in yield of oilseed rape, resulting from the use of herbicides. Depending on treatment, the effects of weed control on yield varied between -9.2 dt/ha to +326 dt/ha with a mean of +3.1 dt/ha (+10.2 per cent) compared to 'non-treated'. 23.5 per cent of all treatments caused yield reductions. This resulted in a mean net grain of 109 DM/ha with a range from -1127 to +2937 DM/ha. According to the relationship grain price/control cost for 1989, 44.1 per cent of the treatments were not profitable. Strong effects of varying weather conditions of the years on the yield response due to weed control were observed. They can be more important than effects of the weed infestation (measured as percent weed coverage). Comparable to the effects of weed infestations are those of regions, soil types, crop coverage and weed species. The relationship between weed coverage and yield is described with linear regressions. Only 8 per cent of the variance could be described with this approach, therefore it is inappropriate for the determination of economic thresholds
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