When herbicides travel: U-M team explores ecological effects of dicamba
By Kelsey Keeves
Herbicides help farmers and home gardeners eradicate difficult weeds and maintain healthy crops. But what happens if they don’t stay in their own lane?
Dicamba, an herbicide commonly used by farmers who grow crops like soybeans and corn, tends to drift from its targeted area. Drift occurs when herbicide sprayed on target plants travels onto nearby fields, gardens or wild plants. Warm temperatures can increase this movement and raise the risk of damage to plants and pollinators such as honeybees and paper wasps.
Regina Baucom, University of Michigan professor of ecology and evolutionary biology, and her colleagues are conducting experiments in partnership with U-M’s Matthaei Botanical Gardens to study the possible outcomes of this off-target movement and how to protect the crops, plants and pollinators affected.
“When the dicamba drifts, it leads to neighboring farms getting hit,” Baucom said. “There’s a cupping leaf morphology that you will see on exposed soybean plants, meaning that you can identify drift fairly easily and, in some cases, it will lead to reduced yield and consequently, reduced revenue for farms.”
The fact that chemicals used to kill weeds can be harmful to the environment is well-known to the average farmer, gardener and consumer. However, as chemical companies frequently update formulas and offer new chemical compounds, the many ways these herbicides affect crops, local plants and pollinators are difficult to measure.
“When the dicamba drifts, it leads to neighboring farms getting hit. There’s a cupping leaf morphology that you will see on exposed soybean plants, meaning that you can identify drift fairly easily and, in some cases, it will lead to reduced yield and consequently, reduced revenue for farms.”
Baucom and her team are working to quantify these effects and explore potential solutions. The U-M researchers are studying several effects of herbicide exposure, including delayed plant growth, soil microbiome disruption and harm to pollinators.
“We need to ensure that if we’re using herbicides, they don’t drift to unintended areas. And making sure that we’re not impacting our groundwater or causing weeds to develop a resistance to a particular herbicide,” Baucom said. “But that involves a lot of study, and from that study, the development and translation of effective regulations.”
In their initial research, they studied six plant species, including three common crop weeds (morning glory, wood sorrel, prickly sida), and three common prairie species (tall tickseed, black-eyed Susan, New England aster), to determine if dicamba was detectable in the nectar and pollen of the nontarget plants, how it influenced pollination biology and whether pollinators behaved differently toward plants sprayed with dicamba.
The next phase of their project expands on their initial research to 19 plant species, utilizing a field at the Matthaei Botanical Gardens. The plants used are a mix of perennials called a prairie strip, developed by researchers at Iowa State University and Michigan State University. Prairie strips are mixes of perennial species placed along farm field borders, designed to support pollinators, reduce runoff and improve biodiversity.
Baucom and her team will use control plots to expand the scale of their initial research, assessing how the dicamba drifts and how the addition of dicamba influenced the normal microbial community. To achieve this, she is collaborating with researchers across U-M to study the broader ripple effects of herbicide drift.
“What makes the University of Michigan an amazing place to do this work is the people who are here and what they are able to bring into this project,” Baucom said.
Noah Webster, research associate professor in U-M’s Institute for Social Research, is working in partnership with Jennifer Blesh, a resident faculty member at Michigan State University’s W.K. Kellogg Biological Station, to develop surveys that ask farmers about their use of dicamba and inform them about the possible benefits of using prairie strips.
Elizabeth Tibbetts, professor of ecology and evolutionary biology, and David Sherman, professor of chemistry, are utilizing the data generated by the field experiment to explore how dicamba can have ripple effects on the local ecosystem.
“When insects get exposed to herbicides, they don’t necessarily die, but their behavior can be altered, so I was really excited that Liz was interested in pursuing how bumblebee or wasp behavior might be different when they get exposed to this increasingly common herbicide,” Baucom said. “And David is focused on a natural product synthesis and can develop techniques for identifying dicamba and other chemical inputs in nature, like nectar and pollen. And so it was just this perfect alignment.”
Sherman is also the Hans W. Vahlteich Professor of Medicinal Chemistry and professor of medicinal chemistry in the College of Pharmacy, professor of microbiology and immunology in the Medical School and research professor at the Life Sciences Institute.
They are also working with Luis Zaman, assistant professor of complex systems and ecology and evolutionary biology, to analyze the data collected and discover the plant-pollinator interactions and how networks are changing.
“We want to know how those natural normal flowering and plant-pollinator networks might be disrupted because of the dicamba exposure,” Baucom said. “In collaboration with Luis, we are using ecological modeling and machine learning to determine which prairie species are the most resilient to this influx of dicamba.”