Linda Geist

COLUMBIA, Mo. – Producers should prepare for more complexity in herbicide requirements and registrations in 2023 and beyond, says University of Missouri Extension weed scientist Kevin Bradley.

The Environmental Protection Agency has proposed changes to atrazine labels that would have great impact, says Bradley. Atrazine is an effective and inexpensive herbicide used to kill broadleaf and grassy weeds in the majority of Missouri corn and sorghum crops.

EPA says its five proposed changes to atrazine labels would decrease atrazine runoff from treated fields. Revisions would restrict annual application rates, application timing based on precipitation and soil saturation and would prohibit all aerial applications. Growers could choose a “picklist” combination of measures when using atrazine in certain watersheds.

“If approved, this could be a substantial change in the way we use atrazine in Missouri,” says Bradley.

Additionally, this past spring producers were introduced to a picklist of required mitigation measures that must be implemented before applying the Enlist herbicide products. Bradley says to expect more of these kind of requirements on future herbicide labels.

Many of these changes are a result of a new position that EPA has taken with regard to its enforcement of the Endangered Species Act. This act requires that EPA evaluate pesticides for potential negative effects on federally listed endangered and threatened species and their habitats and must assess a pesticide’s potential for drift, leaching, runoff and volatility exposures.

Bradley says there are currently more than 1,600 species on the EPA’s endangered species list. One species that is not on the list yet is the monarch butterfly, Bradley says. In July 2022, this migratory butterfly gained a spot on the Red List of Threatened Species maintained by the International Union for Conservation of Nature, an environmental network whose members represent 160 countries. If moved to EPA’s list, it could have a significant impact on the use of weed management tools in the U.S.

The Endangered Species Act considers only the harmful effects of weed management options, Bradley says. It does not weigh the benefits of pesticide use.

Because of increasing regulations, it is important to follow labels and regulations precisely, he says. Follow integrated management practices that don’t rely on a single mode of action.

Approach herbicides as one tool in your weed management toolbox, not a “be all,” says Bradley. As technology evolves, expect more benefits and more complex regulations.

Follow weed management updates at, Mizzou Weed Science on Facebook or @ShowMeWeeds on Twitter. Contact Bradley at or 573-882-4039.

Note: An earlier version of this article misstated the number of species on the Environmental Protection Agency's endangered species list.

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