Enlist Duo, a Corteva Agriscience herbicide that is a mixture of 2,4-D choline and glyphosate, mostly survived legal challenges in a 9th U.S. Circuit Court of Appeals opinion Wednesday that will allow its continued use.

The ruling was in stark contrast to the court’s June 3 decision vacating the registrations of dicamba herbicides Xtendimax, FeXapan and Engenia, which sent shock waves through the grower community before the Environmental Protection Agency allowed continued use of the products through July 31.

Enlist Duo is registered for use on genetically engineered corn, cotton and soybeans in 34 states.

In the decision, the court kept the registration in place but sent it back to EPA to “address the evidence that monarch butterflies may be harmed by the destruction of milkweed on target fields,” an analysis that EPA will use to determine whether the herbicide causes any “unreasonable adverse effect” on the environment, as specified in FIFRA — the Federal Insecticide, Fungicide, and Rodenticide Act.

“EPA’s error in failing to consider harm to monarch butterflies caused by killing target milkweed was not ‘serious,’” the court said, quoting a previous 9th Circuit opinion.

“Moreover, given the technical nature of EPA’s error, EPA will ‘likely be able to offer better reasoning’ and ‘adopt the same rule on remand,’” the court said, again quoting a previous opinion.

Corteva said it is pleased with the decision. "The registration of Enlist Duo remains in place and this leading weed control product can continue to be sold and used by farmers," the company said. "Corteva is confident in the sustainability and effectiveness of Enlist Duo and we are committed to helping farmers continue to realize the benefits of the Enlist Weed Control System, which provides exceptional weed control in corn, soybeans and cotton with near-zero volatility, reduced potential for physical drift and improved handling characteristics."

The decision was not unanimous. One judge, Paul J. Watford, agreed that EPA violated FIFRA requirements with regard to the product's potential harm to the monarch, but also said that in his view, “EPA also violated the Endangered Species Act by failing to use the best scientific data available to assess whether Enlist Duo will adversely affect threatened or endangered species.” He would have vacated both the 2014 and 2017 registrations.

A coalition similar to the one that challenged the dicamba registrations also filed suit over Enlist Duo, largely alleging ESA violations. The groups in the coalition include the National Family Farm Coalition, Family Farm Defenders, Beyond Pesticides, Center for Biological Diversity, Center for Food Safety, and Pesticide Action Network North America. The Natural Resources Defense Council filed a separate petition focused on alleged FIFRA violations.

The court rejected all the arguments put forth by the NFFC coalition and most of NRDC’s.

Center for Food Safety Legal Director George Kimbrell said the court wrongly upheld EPA’s decision not not consult with federal wildlife agencies about the effects of approving the herbicide on more than 500 threatened and endangered species. The court upheld EPA’s finding that approval of the registration would have “no effect” on listed plants and animals.

"The panel held that the EPA did what the ESA required it to do: assess risks to determine whether the exposure of protected species and critical habitat to potentially harmful chemicals would have any possible effect,” according to a summary of the decision prepared by court staff. “The panel concluded that EPA’s ultimate ‘no effect’ findings, and adoption of mitigation measures, were not arbitrary, capricious, or contrary to law.”   

"The panel majority’s unprecedented decision is contrary to controlling law and established science, and Center for Food Safety is analyzing all legal options, including seeking a full court rehearing,” Kimbrell said.

Stephanie Parent, a Center for Biological Diversity attorney involved in the case, said, “We’re extremely disappointed because this ruling blatantly ignores the fact that the EPA relied on data so faulty it was rejected by the National Academy of Sciences. As the dissenting judge pointed out, the research the EPA cites does not even qualify as scientific data. And it ignores well-documented science showing Enlist Duo harms endangered species like Hine’s emerald dragonflies and Fender’s blue butterflies.”

The court also rejected NFFC petitioners’ argument that EPA’s rationale for limiting the ‘action area’ to the treated field was not sound. In addition, the panel rejected NFFC petitioners’ argument that EPA violated its duty to insure no ‘adverse modification’ of ‘critical habitat’ by relying on its 2016 risk assessment.”

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The court said EPA conceded it mistakenly cited FIFRA’s “conditional” registration standard in approving the registration in 2017, but said the error was harmless.

“The panel held that the error did not show that EPA lacked substantial evidence to support its conclusions,” according to the summary.

Other conclusions reached by the court:

  • The panel rejected the argument that EPA failed to consider that Enlist Duo would increase the use of glyphosate over time,” according to the summary. “The panel held that substantial evidence supported EPA’s conclusion that neither the initial 2014 registration of Enlist Duo — nor the subsequent approvals for new use — will increase the overall use of glyphosate.”
  • “The panel rejected petitioners’ contention that EPA failed to properly consider 2,4-D’s volatility — i.e., its tendency to evaporate into a gas and drift to non-target plants. The panel held that EPA reasonably relied on studies to support its conclusion that the volatility of 2,4-D choline salt will not cause … unreasonable adverse effects on the environment.
  • “The panel rejected NFFC petitioners’ contention that EPA should have accounted for the potential synergistic effect” of mixing Enlist Duo with glufosinate. “The panel held that this concern was speculative.”

The judges in the majority were N. Randy Smith and Ryan D. Nelson. Nelson wrote the opinion and Smith concurred.

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