Attenuating the environmental impacts of herbicides

In recent years, soybean fields, along with other crops and trees throughout the Midwest, have been more affected by herbicide drift, particularly those grown from seeds that are not herbicide-tolerant. Unintended drift can cause leaves curling and shrivelling, which can permanently damage a crop.

Kimberly M. Parker assistant professor of energy and environmental chemical engineering, is creating a framework that will help researchers understand the interactions of different chemical agents in herbicide formulations. Stephen M. Sharkey (a fourth-year doctoral candidate in Parker’s laboratory) and Brent J. Williams (associate prof of energy, environmental, and chemical engineering) are her collaborators in this project. Their outlook was published by the journal Environmental Science & Technology Nov. 23.

In 2020, about 90% of all corn, cotton and soybeans planted in the United States were genetically modified to tolerate one or more herbicides, such as glyphosate, dicamba or 2,4-dichlorophenoxyacetic acid (2,4D). Sharkey found that herbicides used on tolerant crops have seen an increase in their use. Before the release of dicamba tolerant crops in 2014-15, dicamba was only used on 2% of all U.S. soybeans. In 2017-18, however, dicamba was used 21% of all U.S. soybeans.

The herbicides 2,4D, dicamba, and 2,4D can affect nontargeted crops unintentionally via herbicide dust. This is either primary drift or secondary drift. Primary drift occurs usually within a few hours of application, when sprayed droplets containing herbicide molecules are carried by the wind to off-target plants.

Secondary drift is when herbicides change from a liquid to a solid state to a vapor. The herbicide then drifts away from the crops affected by temperature, wind, moisture, and herbicide formulation. Volatilization is the process of converting from a liquid to a vapor. This can be worsened when herbicide-tolerant crops are treated later in the season with dicamba or 2,4D. This is because the plants are larger and cover more soil.

Although there are regulations regarding when and how to spray herbicides, drift is still a problem that has prompted a number of lawsuits in recent times. These lawsuits led to the removal of several dicamba products from use and their re-approval by U.S. Environmental Protection Agency.

Dicamba is a chemical compound that contains an amine. This chemical agent is intended to keep the herbicide from volatilizing into atmosphere.

Sharkey, who has previously published a paper about amines in dicamba formulations, stated that “we want to try and figure out why these formulations possess different volatility levels.” “Our focus was on the amines in dicamba formulations, and how their chemical properties impact dicamba’s volatility.

The review also looked at the impact of genetically modified crops on herbicide use. They discovered that herbicide-tolerant crops can have an impact on the use and practices of herbicides. The use of 2,4D and dicamba has been reduced, but dicamba is still being used more often since the introduction of crops that can tolerate them. After 2015’s introduction of dicamba-resistant crops, the use of dicamba grew by 2.3 in just one year.

Sharkey also reviewed data on the different herbicides, as well as the regulations and deregulations governing how they are applied. To reduce drift, the EPA limits the use dicamba and 2,4D. However, soybean and corn regulations have remained relatively unchanged since 2014. Other requirements to reduce drift include limiting the type of nozzle used for spraying herbicides, as well as a buffer area.

Parker stated that in order to address the challenges posed by herbicides drift, it is necessary to continue making progress in designing chemical formations and understanding the impact of herbicides once they enter the atmosphere. “By identifying factors that contribute herbicide drift and identifying the atmospheric processes that impact its impact, we can develop new solutions to stop it,” Parker said.