Over the past 10 years, genetically modified (GM) crops have aroused intense criticism and fear regarding potential environmental and human health impacts. At the same time, GM crop area worldwide has increased more than 60-fold to over 100 million hectares in 22 countries during 2006. Accounting for roughly 80 percent of this area are crops that have been genetically engineered to resist the herbicide glyphosate, popularly known as Roundup. Now, as modern agriculture has become exceedingly dependent on this single chemical, glyphosate resistant weeds have begun to appear and are spreading around the globe. A recent article in Science, "A Growing Threat Down on the Farm," investigates the key aspects this issue.
Glyphosate in Agriculture
Glyphosate has been a popular herbicide for decades, long before the first GM seed was planted on a commercial farm. While extremely lethal to hundreds of different kinds of weeds, the chemical is considered harmless to animals and insects and unlikely to leach into water systems, making it relatively environmentally sustainable compared to other herbicides. Furthermore, the use of glyphosate reduces the need for other, more energy-intensive and environmentally destructive weed control strategies, such as tilling the soil before planting to bury residual weed seeds. It is estimated that no-till farming practices can reduce topsoil loss by more than 80 percent relative to conventional tillage.
Global Area of Biotech Crops by Trait (Million Hectares)
Source: Robert F. Service (25 May 2007). "A Growing Threat Down on the Farm." Science 316 (528), 1114.
Glyphosate Resistant Crops
The first glyphosate-resistant (GR) crop, "Roundup Ready" soybeans, became commercially available in 1995, followed shortly by GR canola, cotton, corn, sugar beets, and alfalfa. Only 12 years later, over 90 percent of soybeans and 60 percent of corn planted in the United States are now glyphosate-resistant. As a consequence, an increasing number of farmers are relying exclusively on glyphosate for their herbicide needs, as opposed 20 or more different chemicals used on a typical farm just a decade ago.
The resulting selective pressure for weeds to develop resistance to glyphosate has been enormous, and now roughly a dozen resistant varieties have been documented. Although the presence of these "superweeds" has yet to significantly disrupt farming systems, many agricultural experts suspect that within a few years the weeds could take over.
Number of Evolved Glyphosate-Resistant Weed Species
Source: Robert F. Service (25 May 2007). "A Growing Threat Down on the Farm." Science 316 (528), 1114.
Finding a Solution
Agricultural researchers are investigating numerous potential solutions to this growing threat. For some, the answer lies in developing new crop varieties that are resistant to herbicides other than glyphosate. Others are working on engineering crops that are resistant to even higher levels of glyphosate, although this might provide only short-term relief, as it could increase the selective pressure on weeds to develop resistance in the long-run. In the meantime, incorporating some traditional resistance-management strategies of rotating crops and using a variety of different herbicides could prolong glyphosate's effectiveness. Overall, this experience will perhaps encourage greater caution surrounding the rapid adoption of biotech agriculture, and especially concerning overdependence on a single variety of crop or chemical.
RELATED LINKS:
Biotechnology Fact Sheet from the U.S. Department of Agriculture
Biotechnology in Food and Agriculture (United Nations Food and Agriculture Organization)
Sierra Club Genetic Engineering Committee Report
EarthTrends
Agriculture and Food searchable database
News: Genetically Engineered Crops May Boost African Agriculture
