Potential agroecological implications of second generation herbicide resistant GM crops

Background/Question/Methods

Agricultural weed management has become entrenched in a single tactic, herbicide-resistant crops, and needs greater emphasis on integrated practices that are sustainable over the long term. In response to the outbreak of glyphosate-resistant weeds, which now number 21 species infesting some 6 million hectares of arable fields, the seed and agrichemical industries are developing crops that are genetically modified to have combined resistance to glyphosate and synthetic auxin herbicides. This technology will allow these herbicides to be used over vastly expanded areas and will likely create three interrelated challenges for sustainable weed management. First, crops with stacked herbicide resistance are likely to increase the severity of resistant weeds. Second, these crops will facilitate a significant increase in herbicide use, with potential negative consequences for environmental quality. Finally, the short-term fix provided by the new traits will encourage continued neglect of public research and extension in integrated weed management. However, we ask, can we expect agricultural weed management to break out of this singular tactic approach, and if so, what changes are needed?

Results/Conclusions

Rather than developing a system that relies so heavily on a singular herbicide-based tactic, integrated weed management could be used to reduce weed populations and selection pressures that drive the evolution of resistant weeds. In addition, such an approach would greatly limit the spillover effects of the singular herbicide-based approach. In integrated weed management, tactics such as crop rotation, cover crops, competitive crop cultivars, and judicious use of tillage, and targeted herbicide application are used together to achieve weedy plant suppression.  Companies have recently begun applying for the registration of this new generation of genetically modified herbicide resistant crops. In order to achieve robust, sustainable methods of weedy plant management we advocate the following concrete policy steps to ensure that we learn from our problematic experiences with glyphosate resistance.  Those policies include US Environmental Protection Agency mandated resistant weed management plans, fees discouraging single-tactic weed management, improved grower education programs implemented through industry-university-government collaborations, and environmental payments that connect integrated weed management to broader environmental goals.