02 Jun EPA Revokes Enlist Duo Registration
Reference: http://www.agriculture.com/crops/pesticides/herbicides/epa-revokes-enlist-duo-registration_179-ar51371
If you were neck-deep in herbicide-resistant waterhemp or Palmer amaranth this year, you might have to wait a while for a new tool to help manage them.
The Environmental Protection Agency (EPA) has revoked its registration for Enlist Duo, the herbicide component of Dow AgroScience’s Enlist Weed Control System.
Pending regulatory approvals from countries like China, Dow was set to launch the Enlist system in 2016. Dow developed the Enlist system in response to the proliferation of weeds like waterhemp and Palmer amaranth that resist glyphosate and other herbicide modes of action.
The system’s trait portion confers resistance to glyphosate and 2,4-D in corn and soybeans and to “fop” herbicides in corn. The herbicide portion called Enlist Duo combines a new 2,4-D formulation called 2,4-D choline with glyphosate. Dow officials say 2,4-D choline slices off-target movement potential compared to existing 2,4-D ester and 2,4-D amine formulations.
Those plans are now in jeopardy. In a prepared statement, EPA cited the combination of 2,4-D choline and glyphosate could result in greater toxicity than expected to nontarget plants, including those classified as endangered species. EPA stated Dow had not provided this information to it prior to EPA issuing the Enlist Duo registration.
In a prepared statement, Dow responded:
“Dow AgroSciences is confident in the extensive data supporting Enlist Duo herbicide. We are working with EPA to quickly provide further assurances that our product’s conditions of registered use will continue to protect the environment, including threatened and endangered plant species.”
Synergy
EPA’s move to revoke Enlist Duo’s registration basically boils down to synergy between the herbicide’s glyphosate and 2,4-D choline mix. From a weed control standpoint, synergy that betters each herbicide can help manage more weeds.
“There can certainly be a benefit for mixing herbicides together for broad-spectrum weed control,” says Aaron Hager, University of Illinois Extension weed control specialist. “If 2,4-D is weak on smartweed, for example, glyphosate can increase control.”
It can be a different story for species like endangered plants, though. Even if endangered species are not impacted by each herbicide alone, it’s the synergistic impact of two chemicals working together and potentially adversely impacting endangered species that gives environmental groups concern regarding Enlist Duo.
“The principal argument we made is that EPA had not examined or complied with the law, with respect to looking at the impact of Enlist Duo on endangered species,” says Paul Achitoff, managing attorney for Earthjustice, a San Francisco-based environmental law organization. Earthjustice helped spearhead a legal challenge in October 2014 by a coalition of groups, including the Environmental Working Group, to the registration of Enlist Duo.
What court documents say
According to San Francisco-based U.S. Ninth Circuit Court documents, EPA initially found no indication of synergism between glyphosate and 2,4-D choline that adversely impacted mammals, freshwater fish, and freshwater invertebrates. “It is reasonable to assume that there are no synergistic interactions for taxonomic groups that were not tested, including plants,” stated the EPA in court documents.
Initially, EPA believed a 30-foot buffer around fields on which Enlist Duo had been applied would be sufficient to not harm nontarget organisms.
However, EPA said it discovered that Dow made claims of “synergistic herbicidal weed control” in patent applications. Following patent application review, EPA sent Dow a letter on October 13, 2015, that said the claimed synergism between 2,4-D choline and glyphosate could affect EPA’s assessment of drift for avoiding impact to nontarget organisms — including those listed as endangered. That was a basis for EPA revoking Enlist Duo’s registration.
What now?
There is precedent for EPA’s latest move. A 2015 case brought before the Ninth Circuit Court — Pollinator Stewardship Council v. EPA — prompted the court to pull EPA’s unconditional registration of sulfoxaflor, an insecticide also manufactured by Dow and marketed under the names of Closer or Transform. Sulfoxaflor is a sulfoximine, a subclass of neonicotinoid insecticides that are currently being scrutinized for negatively impacting pollinators.
However, court documents state EPA could reach a different conclusion for sulfoxaflor registration if it obtains additional studies on the product the court found lacking.
That may be the case for Enlist Duo. New information could lead EPA to adopt different restrictions for use of Enlist Duo, but still permit its use.
“Specifically, this could result in changes to the width around application areas of no-use buffer zones that EPA imposed to protect unintended plants, including those listed as endangered,” said EPA in a prepared statement.
120 million reasons
For farmers like Todd Hanten, Goodwin, South Dakota, approval for a product to better manage herbicide-resistant weeds can’t come too soon. A trip to Tennessee to pick up a tractor he purchased in 2010 was an eye-opener to the adverse impact Palmer amaranth was having in that state’s soybean production. In 2011, Larry Steckel, University of Tennessee Extension weed specialist, calculated that glyphosate-resistant weeds like Palmer amaranth were costing Tennessee soybean farmers $120 million annually.
“It was just a scared, sick feeling,” says Hanten. “I couldn’t believe they (Palmer amaranth infestations) were that bad.”
That caused him to reconsider his weed control strategy and adopt use of preemergence residual herbicides in current weed control strategies with the hopes of complementary new postemergence technologies soon hitting the market.
“I was hoping a system like Enlist would soon be available,” he says. “These weeds will be tough to control without new technologies.”
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