Restrictions designed to limit off-target dicamba damage to crops and other plants did not put a halt to widespread complaints of such damage in 2021, EPA said in an ecological risk assessment released Thursday.

The 2020 application restrictions, including buffer zones and cutoff dates, were supposed to significantly reduce the risk of drift and runoff, EPA said, but EPA received nearly 3,500 incident reports for the 2021 growing season of damage to non-dicamba tolerant soybeans, "numerous other crops, and a wide variety of non-target plants in non-crop areas including residences, parks, and wildlife refuges,” the assessment said.

Looking at the impact on plants, EPA said “the combined evidence from field studies and incident data indicates that there may be off-site movement of dicamba via run-off, spray drift, and volatility from the use of dicamba, particularly for OTT [over-the-top] use on [dicamba-tolerant]-plants. In terms of spray drift, modeling suggests that off-field [level of concern] exceedances can extend > 1000 ft from the downwind edge of the treatment field after ground application (> 2600 ft for aerial applications).”

The ecological risk assessment was released along with a human health risk assessment completed a year ago that found occupational inhalation risks of concern for mixing/loading of dry flowable formulations for aerial and groundboom applications. “EPA found no dietary, residential, aggregate, or post-application risks of concern,” the agency said in announcing release of the risk assessments.

The assessments are part of the agency’s registration review for dicamba, which is sold as Xtendimax, Tavium and Engenia by Bayer, Syngenta and BASF respectively. Both soybean and cotton growers and environmental groups have sued the agency over its 2020 registration decision. The growers contend that the extensive restrictions are not justified, while the environmental groups say the data do not support the herbicide’s approved uses.

A federal court of appeals in 2020 struck down EPA's dicamba registrations, forcing the agencies to conduct new analyses and resulting in further restrictions on the products’ use when they were re-approved later that year. For this season, EPA approved new cutoff dates in Iowa and Minnesota. Complaints of off-target damage continue to be made, however.

Asked about dicamba damage, a Bayer spokesperson said the company has “received fewer reports of potential off-target movement than last season at this point. Each field and each situation is unique, and there are a range of potential contributors to the leaf symptomology being reported, which is why we believe it is important to thoroughly evaluate each case to understand the facts, including the scope and severity of the observed symptomology and the potential causes.”

The company has proposed an amendment to the Xtendimax label that would add restrictions to certain counties occupied by federally listed threatened or endangered species.

“We are continuing to communicate with the EPA about our proposed amendment, which we believe help address the EPA’s stated concerns,” the spokesperson said. “In the meantime, we continue to examine all our options to help ensure this vitally important tool remains available for our customers in 2023 and beyond. 

Dicamba’s current registrations are good through 2025. EPA said it expects to issue a proposed interim decision in 2023, which “may include potential risk mitigation to address any potential risks of concern identified” in the draft assessments.

“EPA is reviewing whether OTT dicamba can be used in a manner that does not pose unreasonable risks to non-target crops and other plants, or to listed species and their designated critical habitats,” EPA said. “EPA is also evaluating all regulatory options for addressing future dicamba-related incidents.”

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EPA’s ecorisk assessment said that “in general, the risk conclusions … are consistent with those identified in past national-level risk assessments for dicamba.” However, there are some “notable exceptions,” including “recently submitted toxicity data [that] indicate a previously unidentified potential chronic risk concern for adult honey bees from all uses on non-DT plants with application rates higher than those EPA evaluated in its 2020 assessment of DT-plant uses.”

In addition, the risk assessment uses newly submitted toxicity data “that obviates the previously identified chronic risk concern for birds exposed to DCSA in DT-soybean plants, which was based on an assumed toxicity value derived from mammalian data.” DCSA is a degradate of dicamba. 

Updated exposure estimates that account for the combined residues of DCSA and fellow degradate 6-CSA “indicate a previously unidentified potential chronic risk concern for non-listed fish from one use scenario,” EPA said. There also is “a potential risk concern for non-listed terrestrial vertebrate species limited to acute dietary exposure of dicamba to birds and chronic dietary exposure of dicamba (non-DT plants) and DCSA (DT-plants) to mammals.”

Nathan Donley, environmental health science director for the Center for Biological Diversity, said EPA’s findings “confirm dicamba’s widespread harms to plants and animals, particularly in over-the-top applications, and raise grave concerns about the ecological damage caused by the Trump administration’s 11th-hour approval of this dangerous pesticide. The science is clear, and the EPA needs to act with urgency to rein in these uses to protect people and wildlife from this drift-prone poison.”

Donley said the assessment shows dicamba “exceeds the agency’s own level of concern for freshwater fish (chronic), mammals (chronic), birds (acute), terrestrial invertebrates (chronic adult bee, chronic larval bee), and plants (terrestrial and aquatic).”

EPA is accepting public comments on the risk assessments for 60 days.

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