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

Abstract

The potential impact of herbicide-tolerant winter oilseed rape (Brassica napus L.) on future herbicide use was investigated with a simulation model. The 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 population are determined by the ecacy of representative herbicides on individual weed species and by seedbank parameters. Herbicide ecacy is determined 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 either 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) decreased. PrerequisitesThe model (Fig. 1) is empirical and based on alleged relationships, comparative studies between transgenic and non-transgenic crops, and practical experience from current crop rotations. The model requires few growth-related parameters and does not take climatic and soil conditions into 96 K. H. Madsen et al.

Simulating weed management in glyphosate-tolerant crops: greenhouse and field studies

“…In current agriculture, glyphosate is often used pre‐harvest or shortly after harvest to control Elymus repens Gould, but this application is expected to have limited effect on seed bank dynamics of dicotyledon weeds and is therefore not included in the model. The input data included crop yields, decay of the soil weed seed bank and crossing frequency between oilseed rape and Brassica campestris L 4…”

“…The seed bank input is determined by a function of biomass at harvest time, whereas depletion of the soil seed bank is governed by an exponential rate of seed decay and a fraction lost to predation and germination of the seeds 4…”

“…The model used in this study is a slightly modified version of a model developed to predict herbicide use under different scenarios with herbicide‐tolerant oilseed rape 4. The validity of the model has not been experimentally determined because large‐scale use of herbicide‐tolerant oilseed rape has not yet been introduced in Denmark.…”

Herbicide‐tolerant crops in agriculture: oilseed rape as a case study

“…Attempts have also been made to model dierent aspects of the impact of transgenic herbicide-tolerant OSR. These include weed population dynamics (McRoberts et al 1999), the eect of cropping systems on gene¯ow (Colbach et al 1999), simulation of herbicide usage in crop rotations (Madsen et al 1999) and modelling the potential for gene escape through soil seed banks (Pekrun and Lane 1999). The UK Government Research into GM crops also includes an examination of the biodiversity within herbicide-tolerant OSR, maize and sugar beet crops through the`farm scale evaluations' programme (Firbank et al 1999, AEBC 2001.…”

Ethics and genetic engineering – lessons to be learned from GM foods

“…It has, for example, been pointed out that many of the``®rst generation'' GM crops are modi®ed to resist herbicides that are less environmentally suspect than the ones already in use. It has also been argued that these herbicides have the potential to reduce the overall herbicide use in crop rotations involving GM crops such as sugar beet [7] and this latter argument is supported by experience in the USA, where the number of herbicide applications has been reduced in herbicide-resistant soybean and cotton [8]. Despite these developments, the environmental argument enjoys limited public support.…”