Nearly every corn seed planted in Colorado is covered in insecticide. Lawmakers may restrict the chemical

DENVER — Colorado farmers plant tens of millions of corn seeds every year, nearly every one of them covered in a thin layer of insecticide.

The neonicotinoids used in the coatings protect the seed from pests in the soil and, as the crop matures, the chemical is absorbed into the plant’s tissue, where it continues to paralyze and kill insects that chomp on the crop.

Farmers say the insecticide is necessary, but growing concerns about its impact on crucial pollinator species and the wider environment are prompting a push in Colorado for more regulation of the widely used class of chemicals. Environmental advocates plan to seek a bill in the state legislature in 2026 that would limit their use in hopes of protecting pollinators and water quality.

While a draft bill has not yet been made public, the environmental groups working on it said the legislation would ban the use of neonicotinoids without prior approval by inspectors overseen by the Colorado Department of Agriculture.

“This is an existential threat to both our wildlife and our own health,” said Allison Johnson, an attorney with the Natural Resources Defense Council who is working on the policy.

But farmers say that without the insecticide, they would have to resort to more damaging pest-control practices — like treating an entire field with chemicals. If the state were to restrict the use of seeds coated with neonicotinoids — also called neonics — few sources of non-coated seeds would remain for them to buy, they said.

“A lot of farmers only get a couple of paydays a year, so it’s really important to have any insurance you can have in protecting your yields,” said Ashley House, the vice president of strategy and advocacy for the Colorado Farm Bureau. “We really see neonics and coated seeds as an insurance policy.”

Nearly universal use

Along with corn seeds, farmers often use the pesticide as a seed coating on sugar beets, wheat, barley, alfalfa and sorghum. It can also be sprayed on crops, soil or landscaping plants.

Neonics work by binding to insects’ nervous systems and paralyzing or killing them. It’s effective, but it impacts more than just pests.

Other insects — including those crucial to ecosystem health, like bees and earthworms — are also exposed to the chemicals. Because the plant absorbs the insecticide, it can be present in pollen and nectar consumed by pollinators. Even if the chemical doesn’t kill insects, it can disrupt their immune and nervous systems as well as their fertility.

The chemicals also make their way into water supplies and up the food chain, according to a 2020 overview of research about neonics compiled by the U.S. Department of Health and Human Services. One 2017 report found neonics present in three-quarters of 198 honey samples collected from around the world.

“The neonicotinoid compounds occurred at levels considered safe for human consumption, but the contamination confirms the inundation of bees and their environments with these pesticides, despite some recent efforts to decrease their use,” the authors wrote in their abstract.

Scientists created the insecticide to replace others that were more harmful to people, said Lisa Blecker, an instructor at Colorado State University and administrator for the Pesticide Regulatory Education Program. Neonics pose relatively low risks for those using them, especially when applied as a seed coating, she said.

“In terms of humans, neonics are much better for the user,” Blecker said.

But environmental advocates worry about the insecticide’s impact on bees and their long-term accumulation in water and food.

“Neonics are ubiquitous in the environment, in our soils, in our drinking water and streams, which is impacting human health and our environment and wildlife,” said Joyce Kennedy, the executive director of the People and Pollinators Action Network. She’s a leader in the campaign to restrict the use of neonics.

Comprehensive data on neonics’ presence in Colorado water is limited, according to an analysis commissioned by the Natural Resources Defense Council.

Water sampling conducted by the U.S. Geological Survey found measurable levels of one type of neonics in eight water bodies — more than a third of the locations tested for the substance. The locations that tested positive for neonics included Cherry Creek in Denver, the Colorado River near the Utah border, the South Platte River north of Denver and in Kersey, and in three suburban locations near Falcon in El Paso County.

At each of the sites, water samples showed concentrations of neonics above the 10-nanograms-per-liter level determined by the Environmental Protection Agency to damage aquatic ecosystems. One of the Falcon locations registered a concentration of 375 ng per liter, and Cherry Creek recorded a level of 157 ng per liter.

Data on whether the insecticide is present in groundwater is even rarer, though its presence in the South Platte River Aquifer has been well documented, according to the analysis.

Solid estimates of how much neonics are used annually in Colorado don’t exist, Blecker said.

Farmers say the chemical is extremely common — and, for some crops, they struggle to find non-treated seed.

“It’s all really treated seeds,” said Nick Colglazier, the executive director of the Colorado Corn Promotion Council.

‘Like if we just gave antibiotics to everyone’

Lawmakers next year are expected to consider a bill that would ban the use of neonics and neonic-coated seeds unless farmers can demonstrate they need them to combat a specific pest problem and gain regulators’ approval.

That solution is meant to curtail the near-universal use of coated seeds and ensure that the use of the insecticide is necessary, said Henry Stiles, an advocate with Environment Colorado.

“An analogy is, it’s like if we just gave antibiotics to everyone,” he said.

Farmers, however, worry that a restriction on their ability to buy coated seeds would impact their businesses and the country’s food supply.

“That would be devastating. We wouldn’t have anywhere to go,” said Matt Mulch, who farms near Burlington and is a board member of the Colorado Corn Promotion Council.[

The potential alternatives to neonic-coated seeds, he said, are either less effective or more damaging to the environment — or both. The seed coatings are more direct and less likely to leech into the water and soils than a spray applied to an entire field, he said.

“This is one of the valuable tools in our toolbox for crop protection,” Mulch said. “This is a business and we don’t waste money, so if it weren’t important, we wouldn’t spend money on it.”

Proponents of limiting the use of neonic-coated seeds said regulations will put pressure on the seed market to provide non-coated alternatives.

“The choices that are being put in front of farmers are not real choices,” said Johnson of the Natural Resources Defense Council. “It’s essential that we take legislative action to create market conditions to create that choice.”

The policy fix under consideration — led by Democratic state Sen. Katie Wallace— closely resembles a program implemented in Quebec in 2019 that banned the use of neonics and neonic-coated seeds unless prescribed by an agronomist. Two U.S. states — Vermont and New York — followed suit and passed similar laws in the last two years, though neither has gone into effect yet.

“It’s an issue that’s bubbling up across the country,” Johnson said.

More restrictions on the sale of neonics would be a part of a critical ongoing effort in Colorado to protect pollinators, Kennedy said.

“We have to do something,” she said. “We’re headed down the wrong road. We try not to be overly catastrophic in our language, but we are on the precipice of some of these issues where, if we don’t take action, we’ll lose biodiversity.”

Colorado lawmakers in 2023 required sellers of neonic pesticides to be licensed pesticide dealers, which blocked sales by many big-box retailers like Home Depot or Walmart. The pesticides remain available, however, at the more than 400 licensed dealers across the state.

The Colorado Department of Agriculture also offers a tax credit for farmers who use seeds without neonic coatings as part of a program to promote stewardship.

The Colorado Department of Transportation has worked to sow pollinator-friendly plants, and the Department of Motor Vehicles created a license plate to raise money for pollinator conservation. In 2022, lawmakers passed a bill requiring a study of the status of the state’s native pollinators. That study prompted 2024 legislation that gave state wildlife officials the authority to manage and conserve invertebrates.

If the legislature restricts the use of neonics, it’s unclear what alternatives could take their place, said Blecker with CSU. Perfect solutions that ward off pests without risking impacts to other species don’t exist.

“You could probably find something else,” she said. “But it’s always this balance with benefit and risk — because all pesticides, by their nature, are killing, repelling and harming a living thing. So they’re all going to have a problem, basically.”