Ann Arbor Times

A recent study by the University of Michigan has highlighted the impact of dicamba, an herbicide, on pollinators due to its off-target drift. The research, led by Professor Regina Baucom from the Department of Ecology and Evolutionary Biology, was published in the journal New Phytologist.

Dicamba, initially developed in the late 1950s and registered for use in 1962, saw a decline in usage due to its moderate toxicity to humans and wildlife. Farmers shifted to using RoundUp, which contains glyphosate, considered more environmentally friendly. However, with weeds developing resistance to glyphosate, Monsanto (now owned by Bayer) reintroduced dicamba-resistant crops. This move was supported by the Trump administration's reapproval of dicamba use in 2018.

Professor Baucom noted that "one of the reasons dicamba went out of favor is because it’s volatile." The herbicide can drift from targeted fields to unintended areas. This volatility has caused issues for farmers not using dicamba as their sensitive crops like soybeans experienced reduced yields.

The study aimed to investigate if this drift affected weeds and pollinators. It found that plants exposed to dicamba had fewer pollinators nearby and reduced visits for some weed species. Dicamba mimics auxin, a plant hormone crucial for development and growth direction towards light. When exposed to dicamba drift, plants such as soybeans exhibit changes like cupped leaves.

Baucom's team constructed plots with 11 different weed species, exposing some to low levels of dicamba drift while others served as controls. Observations showed that plants in control plots attracted significantly more pollinating insects than those exposed to dicamba.

Baucom suspects that "pollinator abundance and visits decreased because of the damage dicamba caused." Damage included altered plant size and flowering patterns which could disrupt plant-pollinator interactions.

"In the control environment," Baucom explained, "there’s a positive relationship between the number of flowers and pollinator visits." However, this relationship disappeared under dicamba exposure.

The researchers plan further investigations into how dicamba affects prairie strips—native plant areas adjacent to farm fields—through a grant from U-M's College of Literature, Science, and the Arts’ Meet the Moment Research Initiative.