New information about the synergistic effects of glyphosate and 2,4-dichlorophenoxyacetic acid, also known as 2,4-D—the two active ingredients in Dow AgroSciences’ Enlist Duo herbicide—has prompted the Environmental Protection Agency to ask a federal court to rescind EPA’s approval of the controversial mixture.
In a motion filed on Nov. 24 with the U.S. Court of Appeals for the 9th Circuit, EPA says that it may have understated the toxicity of Enlist Duo to plants. “The 30-foot [9-meter] buffer on the approved label may not be adequate to protect nontarget plant species located outside the treated fields,” the agency says.
EPA recently discovered a Dow patent application showing that the two active ingredients in Enlist Duo “are more effective in combination than when applied individually.” The agency told the court that it did not have this information when it approved the herbicide last year for use in a handful of states on corn and soybeans that are genetically engineered to tolerate the two chemicals.
Dow AgroSciences says it is confident that it can address EPA’s concerns in time for the 2016 growing season. “We believe the questions that have been raised about any potential synergy between 2,4-D choline,” which is the salt of 2,4-D used in Enlist Duo, “and glyphosate can be promptly resolved in the next few months,” says Tim Hassinger, Dow AgroSciences president and chief executive officer. The label on Enlist Duo, which specifies conditions for the herbicide’s use, could possibly change, Hassinger adds. “However, based on the ongoing dialogue with EPA, we do not expect these issues to result in the long-term cancellation of the Enlist Duo product registration.”
Farmers are running out of options to combat fast-growing weeds. Many weeds are now resistant to glyphosate after extensive use of that herbicide. But many environmental groups worry that overuse of Enlist Duo will lead to “superweeds” that are resistant to both 2,4-D and glyphosate.
A coalition of such groups, which sued EPA last year because of the approval of Enlist Duo, called the agency’s move to withdraw the approval a huge victory for the environment and the future of food. The groups claim that the combination herbicide’s effects on human health and endangered species have been inadequately studied.
“We will remain vigilant to ensure industry does not pressure the agency into making the same mistake in the future,” says George Kimbrell, senior attorney for the Center for Food Safety, a plaintiff in the lawsuit.
Dow plans to respond to EPA’s motion. The court will then decide whether to grant EPA’s request to vacate Enlist Duo’s approval.