U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version



Published in Ecological Effects of Pest Resistance Genes in Managed Ecosystems.


Crops made resistant to herbicides by biotechnology are being widely adopted in North America and entering other parts of the world. Those containing transgenes that impart resistance to post-emergence, non-selective herbicides such as glyphosate and glufosinate will have the major impact. 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 reduce plant pathogen problems because of the chemicals’ toxicity to certain microbes. There is concern among weed scientists that over-reliance on fewer weed management strategies will result in evolution of resistance to the more useful herbicides and/or population shifts to naturally resistant weed species. Although environmentalists are concerned with the potential impacts of gene flow from transgenic crops to wild relatives, herbicide resistance transgenes confer no fitness advantage outside of fields treated with the herbicide. Thus it is unlikely that they would affect plant populations in natural areas. The next decade should clarify the eventual impact of these powerful new tools on weed science and weed management.