top of page

Appeals Court Remands Enlist Duo Registration to EPA But Does Not Vacate

Updated: Nov 10, 2020

Sprayer in field by United Soybean Board and the Soybean Checkoff
Sprayer in field by United Soybean Board and the Soybean Checkoff

This is not a substitute for legal advice. See here for the site’s reposting policy.

2020 has seen several challenges to pesticide registrations. Earlier in 2020, we saw vacaturs with dicamba registrations for three products. Recently the Ninth Circuit Court of Appeals found an error in the Enlist Duo’s registration details. The court sent the decision back to EPA to relook at the impact of Enlist Duo’s usage on milkweed in target areas. At this time, the product will not be removed from the market.


Enlist Duo is a herbicide developed by Dow Agrosciences which combines 2,4 dichlorophenoxyacetic acid (2,4-D) and glyphosate to improve upon delivering both chemicals separately. In late 2014, the U.S. Environmental Protection Agency (EPA) issued a final order registering Enlist Duo under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and approved the registration of the herbicide again in 2015.

In early 2017, EPA issued another registration decision on Enlist Duo based on claims Dow had made in a patent application. In this registration, EPA approved the use of the herbicide in 34 states for corn and soybeans, approved as a new use for cotton in the same 34 states, and reaffirmed prior registrations in 2014 and 2015. EPA registered the product on a conditional basis but appeared to cite standards related to unconditional registration. These registrations were challenged by groups before the Ninth Circuit Court of Appeals, claiming EPA had applied the wrong standard when registering the herbicide and did not properly assess the harm the herbicide could cause on the monarch butterfly under the Endangered Species Act (ESA).

Registration Under FIFRA

National Family Farm Coalition, Family Farm Defenders, Beyond Pesticides, Center for Biological Diversity, Center for Food Safety, and Pesticide Action Network North America claim that EPA used the wrong standard in originally approving Enlist Duo back in 2104; the group contends that EPA used the more lenient “conditional” registration standard instead of a more stringent “unconditional” registration standard. An unconditional registration of a pesticide requires EPA to review all relevant data available and determine no additional data is needed to make a decision. When reviewing the relevant data for an unconditional registration, EPA must determine the pesticide will not generally cause any unreasonable adverse effects on the environment when used according to widespread and commonly recognized practices.

A conditional registration or amended registration allows for use of the pesticide in special circumstances. To conditionally register or amend an existing registration, EPA must determine if the data submitted by the applicant is satisfactory, pertains to the proposed additional use, and would not present a significant increase in the risk of any unreasonable adverse effect on the environment. At the same time, when an active ingredient has already been registered, EPA takes the view that a complete review of existing data will use the criteria for conditional registration. In this case, Enlist Duo would include two active ingredients of glyphosate and 2,4-D and EPA only needed to complete a review of the existing data for those two active ingredients.

The Ninth Circuit found the claims that EPA incorrectly applied the wrong standard, conditional instead of unconditional, to be unpersuasive. First, the group raising the claim had never raised it during the administrative process and was viewed to have waived the argument. Although the court viewed this claim as waived, the court still reviewed the arguments raised. The Ninth Circuit rejected this argument.

Image of sprayer in field by United Soybean Board
Image of sprayer in field by United Soybean Board

The court also rejected arguments that EPA failed to look specifically at potentially unreasonable adverse impacts on the environment from increased glyphosate. EPA argued and the court agreed that FIFRA allows for an ingredient-by-ingredient review. EPA can do a review similar to the approved prior usage covering whether the proposed use will significantly increase any unreasonable adverse effect on the environment. The court found substantial evidence to support EPA’s approval of the usage of glyphosate in Enlist Duo. The court also rejected claims that EPA had failed to properly consider the 2,4-D’s volatility. The court found no evidence to demonstrate EPA reached the wrong conclusion. Finally, the court rejected arguments that EPA should have considered the potential synergistic effect of mixing Enlist Duo with glufosinate. The court found no evidence in the record of this happening during the past five years the product was on the market, and that EPA can do a review of the pesticide product when it becomes necessary.

The court then turned to claims EPA lacked substantial evidence for 2014, 2015, and 2017 which account for the impact of increased usage of 2,4-D on milkweed and the harm it would have on monarch butterflies. The plaintiffs argued that EPA failed to assess the risks of 2,4-D use in destroying milkweed in target fields. EPA acknowledged it did not consider this, and the court rejected EPA’s arguments for not looking at the potential harm to milkweed on target fields to determine if such an impact would be unreasonable.

Finally, the court rejected all of the ESA claims brought by the plaintiffs. The court found that EPA finding no effect for plants and animals was not arbitrary, capricious, or contrary to the law based on the assessments done by EPA. According to the court, the agency followed the law in reviewing the claims under the ESA.

Because the court found an error in the registration decision, it had to determine the appropriate remedy. The court could either vacate the registration, as it did in the dicamba-based herbicide decision earlier in the year, or remand to the agency for better reasoning required under FIFRA. The court went with remanding to the agency and vacating the registration.

Currently, the registration is still before EPA for further analysis of the increased usage of 2,4-D on target areas impacts on milkweed. The product will continue to be on the market and available for growers to utilize. To learn more about this issue, check out this blog post from Brigit Rollins with the National Ag Law Center.



bottom of page