Controversial weedkiller could spell big trouble for monarch butterflies: Report

Environmental group reports over the next year more than 60 million acres of the monarch's US migratory habitat will be sprayed with dicamba

By 2019, a weed killing chemical—designed to be used in tandem with genetically modified cotton and soybean seeds—is projected to be sprayed on more than 60 million acres of monarch butterfly U.S. migratory habitat, according to a report released today by the Center for Biological Diversity.


Citing this potential devastation to monarch populations, which have already decreased an estimated 80 percent over the past two decades, the report calls on the U.S. Environmental Protection Agency not to renew the registration of the weed killer, called dicamba, when it expires at the end of this year.

The concern is the chemical could cause more habitat loss and decreased milkweed, which is the only food plant used by monarch caterpillars. Monarchs winter in Mexico and some warm areas of Southern California and they return to areas throughout the U.S. in the spring.

"America's monarchs are already in serious trouble, and this will push them into absolute crisis," said report author Nathan Donley, a senior scientist at the Center, in a statement.

Donley and colleagues looked at monarch habitat in the U.S. and estimated how much dicamba will be sprayed. In addition to the estimated 60 million acres to be sprayed, an additional 9 million acres could be threatened by the chemical drifting.

The weed killer gained notoriety this year as farmers planted more than 25 million acres with new soybean and cotton seeds genetically modified to be resistant to dicamba. Monsanto, BASF SE and DowDuPont all make dicamba-based herbicides.

In many areas the weed killer drifted onto nearby fields and killed crops, spurring lawsuits in Arkansas, Missouri, Kansas and Illinois. Arkansas banned dicamba; North Dakota, Missouri and Minnesota put restrictions in place.

"In 2017 there were reports of at least 3.6 million acres of off-target, herbicide-induced damage to agricultural crops and an unknown amount of damage to native plants and habitats, including forests," according to the Center's report.

Dicamba is a threat to monarchs because it can destroy flowering plants that provide nectar for adult butterflies as they travel south for the winter and by harming milkweed, which is the "only food source of the monarch caterpillar" and "provides an essential resource for reproduction," stated the report.

"When dicamba's use on [genetically engineered] cotton and soybeans comes up for reapproval later this year, the only responsible thing for the EPA to do is allow that approval to expire," Donley said.

We've reached out to Monsanto to comment on the report.

Print Friendly and PDF
SUBSCRIBE TO EHN'S MUST-READ DAILY NEWSLETTER: ABOVE THE FOLD
From our Newsroom

Editorial: Bicycling is having a moment—let’s use it to make riding more safe and inclusive

As we celebrate a World Bicycle Day like no other, can the U.S. keep the momentum and attention the coronavirus pandemic has brought to bicycling?

Coronavirus, the environment, and you

How the spread of the deadly virus is impacted by climate change, the environment, and our lifestyles.

Climate change creates camouflage confusion in winter-adapted wildlife

Twenty-one species molt from brown to white to survive the winter season. But climate change has created a mismatch between their snowy camouflage and surroundings.

They blinded us with SCIENCE!

From climate change to COVID-19, even the clearest warnings from scientists can misfire with millions of Americans. Pop culture may be a big reason why.

Cutting edge of science

An exclusive look at important research just over the horizon that promises to impact our health and the environment

Above The Fold

Daily & Weekly newsletters all free.