Simulation of herbicide use in a crop rotation with transgenic herbicide-tolerant oilseed rape

The potential impact of herbicide-tolerant winter oilseed rape (Brassica na pus L,) on future herbicide use was investigated with a simulation model. T he model uses a sigmoid function to simulate the growth of crops and weeds that compete for a maximum yield potential. Thresholds for weed control are based upon critical levels of weed biomass, The dynamics of the weed popul ation are determined by the efficacy of representative herbicides on indivi dual weed species and by seedbank parameters. Herbicide efficacy is determi ned by a log-logistic dose-response curve for each species. Simulation of a rotation with winter oilseed rape/wheat/wheat/barley showed contradictory predictions of herbicide use, because herbicide use in a rotation with eith er glyphosate- or glufosinate-tolerant oilseed rape was not reduced in the amount of kg a.i, ha(-1) compared with a traditional treatment, whereas the treatment frequency (number of standard recommended doses per unit area) d ecreased.