Agro-environmental effects due to altered cultivation practices with genetically modified herbicide-tolerant oilseed rape and implications for monitoring. A review

Genetically modified herbicide-tolerant oilseed rape or canola (Brassica napus L.) is at the forefront of being introduced into European agriculture. Concerns have been raised about how genetically modified oilseed rape cultivation and the modified cropping practices might impair the agro-environment. The present review compiles and categorises evidenced and potential agro-environmental effects of cultivating genetically modified oilseed rape and assesses the data quality of published references. Cropping practice changes were identified for (a) the introduction of genetically modified oilseed rape cultivation per se, (b) time, mode and rate of herbicide application, and spraying frequencies, (c) soil tillage and cover crops, (d) crop rotations and (e) coexistence measures to avoid mixing of genetically modified and non-genetically modified cultivation systems. Agro-environmental effects identified are directly linked to the herbicide tolerance technology and may impact ecological processes on various scales. The herbicide-tolerant oilseed rape biology, genotype and co-existence constraints with neighbouring agricultural systems also entail various agro-environmental effects. The potential and especially the well-evidenced adverse effects on the agroenvironment, according to European legislation, require a systematic monitoring of genetically modified oilseed rape. The most evidenced adverse effects to be monitored are persistence and/or spread of feral herbicide-tolerant oilseed rape and volunteers, transfer of herbicide tolerance to wild relatives and decline in agrobiodiversity, and development of herbicide tolerance in weeds, as well as adverse effects on field organisms and/or soil bio-geochemical cycles. Other well-evidenced potential adverse effects include reduced crop rotation options, increased late-season herbicide drift and pollution, and implications for microbial and faunal activities due to altered agrochemical profiles, as well as implications of feral herbicide-tolerant oilseed rape on neighbouring habitats.