EPA finds new risks with dicamba weedkiller

By Marc Heller | 08/18/2022 04:15 PM EDT

The environmental agency’s latest draft ecological risk assessment identified risks to honeybees, in addition to already known dangers to non-target plants.

Bees are seen on a honeycomb cell at the Behaviour, Ecology and Evolution Lab's hives at the University of Sydney in Australia on May 18, 2021.

Bees are seen on a honeycomb cell at the Behaviour, Ecology and Evolution Lab's hives at the University of Sydney in Australia on May 18, 2021. Lisa Maree Williams/Getty Images

The widely used weedkiller dicamba poses a previously unknown risk to honeybees, EPA said in a draft assessment of the pesticide’s potential dangers to wildlife.

In the draft ecological risk assessment released today, EPA said recent toxicity data indicates a “potential chronic risk concern” for adult honeybees exposed to higher levels of dicamba than previously reviewed. There’s also additional risk to fish in limited circumstances, the agency said.

The draft assessment, open to public comment for 60 days, is part of the ongoing routine registration review for dicamba, a popular herbicide farmers use on soybeans and other crops genetically modified to tolerate it. EPA released the draft along with an updated human health risk assessment that echoed earlier findings.


On the other hand, EPA said, new information eased previous concerns about risks to birds from dicamba spread on genetically modified soybeans, and no risks were identified for aquatic nonvertebrates.

Today’s draft addresses only wildlife not federally listed as threatened or endangered, EPA said.

The primary concern with dicamba, EPA said, is exposure to plants when the chemical drifts away from the fields where it’s intended. Since its use on genetically modified crops began around 2016, dicamba has developed a history of killing non-genetically modified crops on neighboring fields, for instance.

“Numerous non-target plant incidents have been reported to be associated with the use of dicamba,” the agency said in a news release. “EPA continues to monitor the incidents information for dicamba.”

Although EPA has approved its continued use, the agency has made label modifications to try to rein in unintended damage — to limited effect. Dicamba’s manufacturer, Bayer, has supported those efforts while rebuffing critics’ call for a ban on so-called over-the-top use on growing crops (Greenwire, Dec. 22, 2021).

The Center for Biological Diversity said in a statement today that the findings underscore the need to further restrict uses of dicamba.

The 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,” said Nathan Donley, the CBD’s environmental health science director.