Farmers who use herbicide-tolerant crops face a growing challenge from herbicide-tolerant and herbicide-resistant weeds, which are evolving and spreading across cropland.
In the southeastern United States , weeds that can tolerate or resist the popular herbicide glyphosate are threatening cotton crops. In the article “Loss of Glyphosate Efficacy: A Changing Weed Spectrum in Georgia Cotton,” (Weed Science Volume 58, Issue 1, 73-79)
Theodore M. Webster and Lynn M. Sosnoskie examine how the use of glyphosate-tolerant cotton (GTC)—created through genetic modification—has affected weed control issues since its introduction in 1997.
The article is featured in the January–February 2010 issue of Weed Science, published by the Weed Science Society of America. As farmers plant more acres of GTC, they are seeing a change in the most prevalent weeds, which now include varieties that tolerate or resist glyphosate.
The two most troublesome weeds in Georgia cotton are:
- Benghal dayflower, which is tolerant to glyphosate and many of the herbicides used in agronomic crops.
- Palmer amaranth, which has developed resistance to many classes of herbicides including glyphosate.
These weeds typically develop in systems without diverse weed control practices. “The management practices necessary for minimizing the development of herbicide resistance have not been widely implemented,” Webster and Sosnoskie write. They see a need for farmers to work toward greater stewardship, which is the sum of the management decisions and practices used to preserve the utility of a crop trait, and try new or varied weed management strategies that often may be more expensive.
“Agricultural practices aimed at delaying or preventing the development of herbicide resistance are not viewed as being economical in the short term and are not readily used by all growers,” they write. “Because herbicide resistance can spread quickly, indiscriminate use of glyphosate may result in a loss of weed susceptibility for all growers, a tragedy of the commons.” Webster and Sosnoskie identify two reasons why growers are not adopting methods that promote glyphosate stewardship:
- The belief that a new technology will be developed to solve the resistance and tolerance problems, although no new herbicides have been introduced commercially since 1998
- The belief that resistance management strategies will be futile because most farmers think herbicide resistance traits are mobile through pollen-mediated transfer and their fields are affected by other nearby farms
The authors outline several possible incentives for cotton farmers, including industry initiatives to promote better glyphosate stewardship and voluntary government farm programs.
However, they say it likely will take a combination of incentives and a move toward new methods to improve weed control.
“Principles of ecological weed management used in conjunction with herbicide-based weed control systems will likely be an important component of future weed management systems,” Webster and Sosnoskie write.
They also identify several areas for future research: how to limit the development of herbicide-resistant and herbicide-tolerant weeds; whether there is a need to limit the use of glyphosate; factors that may improve control and stewardship of herbicide options; how herbicide resistance traits move across the landscape; what factors could be used to determine a species’ risk of developing resistance; and incentives to help improve herbicide stewardship. The full-text article is available at http://www2.allenpress.com/pdf/WEES_58.1_73-79.pdf.
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