The prevalence of Roundup Ready crops has not caused weeds to become resistant to glyphosate; rather, resistance is a function of how glyphosate has been used in RR crops and in other areas. In general, resistance to an herbicide is related to how it is used and the potential for resistance to evolve. Because of the recognized safety and environmental benefits of glyphosate, many farmers relied on it as the sole herbicide to control weeds, and we now know that this practice was not sustainable. Importantly, in cooperation with leading academics, we are making progress in educating growers to use other herbicides and to incorporate non-chemical weed-control practices into their overall weed management program. This increased diversity will lead to a reduction in future resistance.
Additionally, we know that when a weed is resistant, increasing the herbicide rate will not then control it, so more glyphosate will not be effective to control-resistant populations.
Dow AgroSciences is asking the government to approve 2,4-D-tolerant crops, and Monsanto is asking for approval of dicamba-tolerant crops. Both herbicides are effective for controlling weeds that are resistant to glyphosate and for which there are currently few other options. This is why groups like the National Soybean Growers Association, National Cotton Council, Weed Science Society of America and others have written letters to the government in support of both 2,4-D and dicamba. This is important to farmers and to environmentalists who appreciate the benefits of conservation tillage systems, such as reduced pollution of our rivers and streams due to soil erosion. To continue to realize these important benefits (see answer to previous question on benefits), farmers need new herbicide options for managing hard-to-control weeds; otherwise, they would have to consider incorporating tillage operations for weed control and give up some of the benefits already gained by switching to conservation tillage. From a health-and-safety standpoint, both 2,4-D and dicamba have been thoroughly tested and have been approved for agricultural and homeowner uses for over 30 years.