ABSTRACT
Genetically engineered or genetically modified (GM) herbicide tolerant (HT) crops have been widely adopted in many of the countries where they have been commercialised. GM-HT crops offer significant advantages in managing difficult to control weed species and weeds resistant to other herbicides. They have also provided simpler and often more effective weed management. There have also been other advantages in the farming system, such as easier adoption of no-till crop seeding. The majority of GM-HT crops are tolerant to the herbicide glyphosate. This has inevitably resulted in an increase of glyphosate use leading to the evolution of glyphosate resistance in weeds. In some areas, glyphosate resistance has become so extensive that it has had a significant impact on the ability of farmers to manage the weeds. One problem with sustainable weed management in the era of GM-HT crops is the over-reliance on a single herbicide for weed management. This has been driven by the ease of weed management with glyphosate and the fact that often only a single HT trait was introduced into the cropping system. GM crops with stacked HT traits have been developed in recent years. These have the potential to make weed management more sustainable; however, without a change in farmer behaviour this will be unlikely. GM-HT crops need to be included in a diverse system involving a range of weed management practices, rather than reliance on a single herbicide.
