Jun. 1—Federal officials again are considering aerial pesticide spraying in a scenic area of the Rio Chama, despite the backlash a similar plan drew last year from conservationists, tribal advocates and political leaders.

Federal and private landowners have requested 22,500 acres — roughly 35 square miles — be treated to thwart the insects that consume grasses essential for grazing cattle.

Critics worry the chemicals would kill bees, monarch butterflies and other insects vital to the ecosystem. They also fear heavy rains could carry the insecticides into the river.

Pest-control managers haven’t yet decided whether to spray insecticides and will monitor the area in the coming month to see if grasshopper populations grow enough to warrant such treatments.

The U.S. Agriculture Department’s branch in charge of combating invasive pests has had local field technicians conduct a weekly tally of grasshoppers since April in parts of the area to determine their density.

So far, the grasshoppers infest fields by an average of six per square yard, a bit below the eight-per-yard threshold deemed an outbreak that threatens rangeland ecosystems, a USDA official wrote in an email.

“Surveys will continue for the next several weeks and if the populations remain low, no treatments will occur,” wrote William Wesela, national policy manager for the USDA’s Animal and Plant Health Inspection Service.

The agency hasn’t determined yet exactly how many acres would be sprayed from the air should grasshopper populations reach the level of an outbreak, he added.

One difference is that this year the planes would spray diflubenzuron, which kills insects in the juvenile stage, rather than carbaryl, a potent neurotoxin that’s “broad spectrum” or indiscriminate in the species it can harm, including fish and birds that could eat the poisoned insects.

Carbaryl also is carcinogenic to humans — raising concerns about it falling on people rafting or hiking in the area — whereas diflubenzuron is not linked to cancer, according to the U.S. Environmental Protection Agency.

Despite the potential risks to non-targeted species, federal land managers say exterminating grasshoppers is necessary in areas like these that are near ranches.

Aside from depleting grazing pastures, grasshoppers can cause soil erosion and reduce the cover for smaller animals and invertebrates such as butterflies, spiders, caterpillars and worms, federal officials say.

But a watchdog group contends large-scale pesticide spraying, especially from a plane, poses a greater risk to butterflies, spiders, pollinators and wildflowers as well as the nearby river.

“That’s a concern because of drift,” said Sharon Selvaggio, pesticide program specialist for the Xerces Society. “There [are] a lot of sensitive sites nearby as well as in the area.”

The agency in general has improved in forming buffers for aerial spraying, but near the Rio Chama it is not creating enough distance from a wilderness study area and the river itself, even though it’s designated as wild and scenic, Selvaggio said.

The current brand of insecticide the agency would use, which doesn’t exterminate adults, is far from innocuous, she said — it kills butterflies while they’re caterpillars and bees while in their larval stage.

The southern plains bumblebee, which is on the verge of being listed as endangered, would be especially vulnerable to this chemical, Selvaggio said, since bees can gather tainted pollen and take it back to their colonies.

“There’s no way to protect native bees like that flying around the landscape,” Selvaggio said.

The agency’s plans last year to aerially spray 670 gallons of carbaryl near the Rio Chama stirred a public outcry that grabbed the attention of local, state and federal leaders. The controversy led to the Bureau of Land Management, which controls much of the acreage, to cancel the spraying on its tracts to allow more analysis and public outreach.

BLM managers are again expressing skepticism about blanket pesticide spraying.

BLM’s Taos field office has not requested spraying this year and is doubtful it will because of the low grasshopper population reported so far, spokeswoman Allison Sandoval wrote in an email.

BLM officials also don’t believe the USDA’s assessment satisfies the National Environmental Policy Act or is sufficient public outreach, she wrote.

“We therefore do not believe that spraying in 2024 is feasible,” Sandoval wrote.

An Indigenous advocate said a massive spraying could have far-reaching effects on the river, aquifers and watershed, affecting the area’s tribes and downstream users.

“My concern of course is the killing of monarchs, pollinators, fish, the wildlife, fowl and the potential contamination of the watershed,” said Terry Sloan, director of Southwest Native Cultures. “There are a lot [of] people, tribes, nations that rely on the rivers — the Chama and the Rio Grande — and those would have been under threat of contamination.”

Sloan said he worries storms could wash the insecticides into the rivers and carry them to Albuquerque, where they could pollute the aquifer.

Selvaggio and other environmental advocates say if the agency must apply pesticides, ground crews should spot-spray them, minimizing coverage and keeping the toxins from drifting.

But Wesela wrote the agency’s preferred method is to spray aerially.

A plane sprays in a striped pattern, applying the chemical on swaths while leaving adjoining ones unsprayed, he wrote. This avoids other types of insects while catching the highly mobile grasshoppers when they move from untreated swaths to treated ones, he added.

“We apply much less chemical (lower than label rates) to much less area, allowing the beneficial and pollinating insects to have a refuge,” Wesela wrote.

As grasshoppers hatch and grow, the agency looks not only at their density but environmental factors, he wrote. “It is not unusual for many requested acres to go untreated based on actual conditions on the ground.”

But Selvaggio said, realistically, an aerial pesticide can’t be stopped from floating into places not intended for treatments. During one aerial spray in Nevada, the chemicals missed their target by 1,000 feet, she said.

The environmental factors Wesela referred to when describing a spraying plan, Selvaggio said, would include how much it rained recently and how dry conditions are on the ground.

There also are economic considerations such as how productive the rangeland is that the agency seeks to protect from pests, she said. However, there’s little evidence the agency ever bases a spraying regimen on anything except grasshopper density, she said.

Even the density standard the agency uses is questionable, she said. As far back as the early 1990s, entomologists challenged a singular eight-per-square-yard threshold, saying the number should vary depending on the location and should be higher overall, she said.

The federal government can be secretive about pesticide sprayings, and often won’t disclose important data when records are requested — enough so that a recent congressional appropriations bill had a provision requiring the agency to be more open about its spraying activities, Selvaggio said.

Last year, the agency presented the environmental assessment to the public in the spring, but not the specific plan on spraying. That was discovered by a Xerces staffer who was doing a routine search through government documents.

This year, no one knew what the agency had planned until a reporter inquired.

“If it’s on public land, there’s no legitimate reason to withhold that from the public,” Selvaggio said.