New resistant soybean and cotton cropping systems based on the synthetic auxin herbicides give farmers new options for managing Palmer amaranth and other broadleaf weeds resistant to glyphosate. But scientists with the Weed Science Society of America (WSSA) say special precautions are necessary. Auxin herbicides are known to drift and to cause harm to sensitive, off-target broadleaf plants.

“Concerns about drift led the U.S. EPA to issue time-limited registrations for the auxin herbicides dicamba and 2,4-D of two years and five years respectively,” says Kevin Bradley, Ph.D., past president of WSSA and associate professor at the University of Missouri. “The approved product labels have considerable detail on management of drift and other risks and must be carefully followed to reduce off site movement. Unless growers show they can use these herbicides as labeled, the registrations could easily be revoked.”