Abstract
Crops made resistant to herbicides by biotechnology are being widely adopted in North America and other parts of the world. The major impact will be from crops containing transgenes imparting resistance to post-emergence, non-seletctive herbicides for which there is only one commercially successful analogue, such as glyphosate and glufosinate. These products allow the farmer to more effectively use reduced- or no-tillage cultural practices, eliminate use of some of the more environmentally suspect herbicides, and use fewer herbicides to manage nearly the entire spectrum of weed species. In some cases, non-selective herbicides used with herbicide-resistant crops even reduce plant pathogen problems because of their toxicity to some microbes. There is concern among weed scientists that eventual over reliance on fewer weed management strategies will result in evolution of resistance to the more useful herbicides and/or weed population shifts to naturally resistant species. Environmentalists are concerned with gene flow from transgenic crops to closely related wild relatives; however, herbicide resistance transgenes alone confer no fitness advantage outside of fields treated with the herbicide, making it unlikely that they would affect plant populations in natural areas. The next ten years should clarify the eventual impact of these powerful new tools on weed science and weed management.
