Weed resistance to synthetic auxin herbicides

Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non-cropland areas since the first synthetic auxin herbicide (SAH), 2,4-D, was introduced to the market in the mid-1940s. The incidence of weed species resistant to SAHs is relatively low considering their long-term global application with 29 broadleaf weed species confirmed resistant to date. An understanding of the context and mechanisms of SAH resistance evolution can inform management practices to sustain the longevity and utility of this important class of herbicides. A symposium was convened during the 2nd Global Herbicide Resistance Challenge (May 2017 in Denver, CO, USA) to provide an overview of the current state of knowledge of SAH resistance mechanisms including case studies of weed species resistant to SAHs and perspectives on mitigating resistance development in SAH-tolerant crops.The authors are arrayed in alphabetical order because each made substantive contributions to the success of the Weed Resistance to Synthetic Auxin Herbicides symposium convened on May 15, 2017 during the Global Herbicide Resistance Challenge meeting in Denver, Colorado,USA. The symposium organizers and speakerswould like to thank the Global Herbicide Resistance Committee (www .hracglobal.com) for their financial support that made the symposium possible. The authors wish to thank Katrina Nelson, Dow AgroSciences, LLC, for her assistance in manuscript preparation. ™ Trademark of The Dow Chemical Company (‘Dow’) or an affiliated company of Dow. ® Trademark of Monsanto Company