Dicamba drift: New use of an old herbicide disrupts pollinators
An herbicide may "drift" from the agricultural fields where it's sprayed and harm weeds that grow at the edge of the fields, impacting pollinators.
A University of Michigan study examined the effects of the herbicide, called dicamba, and found that plants exposed to dicamba drift had a lowered abundance of pollinators, and that pollinator visits to flowers were reduced for some weeds, but not others. The study, led by U-M professor of ecology and evolutionary biology Regina Baucom, is published in the journal New Phytologist.
Dicamba was developed in the late 1950s and first registered for use in 1962. But the herbicide is moderately toxic to humans and wildlife, Baucom said. Its use fell out of favor, and farmers began using RoundUp on crops that had been genetically modified to tolerate glyphosate, the active ingredient in RoundUp. Glyphosate has generally been considered environmentally friendly.
Dicamba was developed in the late 1950s and first registered for use in 1962. But the herbicide is moderately toxic to humans and wildlife, Baucom said. Its use fell out of favor, and farmers began using RoundUp on crops that had been genetically modified to tolerate glyphosate, the active ingredient in RoundUp. Glyphosate has generally been considered environmentally friendly.
But weeds have evolved resistance to the intense use of RoundUp. The agricultural company Monsanto, now owned by Bayer, turned to dicamba, and developed crops that were resistant to it. In 2018, the Trump administration reapproved its use. Soon after farmers began using the herbicide, other farmers began reporting that their crops were impacted, Baucom said.
"One of the reasons dicamba went out of favor is because it's volatile. A farmer will spray it, and it will go up into the air column or re-volatize, then drift and expose unintended areas," Baucom said.
Farmers who weren't yet using dicamba reported that their crops such as soybeans, which are very sensitive to dicamba, weren't producing their typical yield, she said.
"One of the reasons dicamba went out of favor is because it's volatile. A farmer will spray it, and it will go up into the air column or re-volatize, then drift and expose unintended areas," Baucom said.
Farmers who weren't yet using dicamba reported that their crops such as soybeans, which are very sensitive to dicamba, weren't producing their typical yield, she said.
A monarch butterfly sips from a milkweed. Credit: Regina Baucom, University of Michigan
Weeds grow at the edge of an agricultural field. Drift from the herbicide dicamba could impact pollinator populations in patches of plants such as these. Credit: Regina Baucom, University of Michigan
A bumblebee gathers nectar from a species of Asteraceae, a plant that looks similar to a species used in a study conducted by University of Michigan researcher Regina Baucom. The study examines the impact of the drift of dicamba, an herbicide, on pollinator populations in plants growing adjacent to agricultural fields. Credit: Regina Baucom, University of Michigan