What Newly Approved Herbicides Could Mean For Federal Land

This article is part of The State of Science, a series featuring science stories from public radio stations across the United States. This story, by David Condos, was originally published by KUER.

Invasive plants are a big problem across the western US.

Cunning interlopers like cheatgrass, leafy spurge and red brome can outcompete native vegetation, crowd habitats and steal water and other vital soil nutrients.

Of the 245 million acres controlled by the Bureau of Land Management, harmful non-native plants have already infested 79 million acres—an area larger than the states of Pennsylvania, Virginia and South Carolina combined. That’s why the federal agency felt the urgency to approve seven new herbicides to kill invasives on its land nationwide, said Seth Flanigan, a BLM senior invasive species specialist based in Idaho.

“If we don’t remove this now, what is it going to look like 10 years from now?” he said.

So, what makes these invasive species so devious?

Take cheatgrass, one of the biggest threats in the Mountain West. It can start growing earlier in the season than native grasses, so it gets a head start while the weather is still cold. Like other invasives, it’s also a prolific seed producer, so it can quickly take over the landscape.

“The majority of ecosystems across the West have been impacted by weeds that have changed the composition, structure and function of those ecosystems. It’s a major problem,” said Dr. Cara Nelson, who directs the Restoration Ecology Lab at the University of Montana.

“They affect the abundance of native plants, and those native plants play important roles in providing food and habitat for wildlife.”

Invasives can ramp up wildfire risk, too. Historically, desert landscapes are sparsely vegetated, dotted with shrubs that have bare ground between them. Annual grasses like cheatgrass and red brome can fill in those gaps. That not only adds a bunch of highly flammable fuel, but it also connects the vegetation—which can spread a fire further and faster.

The harmful plants also make things harder for wildlife, like the threatened Mojave Desert tortoises that live in the BLM-managed Red Cliffs National Conservation Area in southwest Utah. Conservation groups already worry about the pressures tortoises and other species in that area face from development because nearby St. George has been one of the nation’s fastest-growing cities in recent years.

But the fight against invasives needs to be done the right way, said Judy Hohman, a board member with the Desert Tortoise Council.

“We’re definitely in favor of the BLM taking measures to halt the introduction and spread and proliferation of non-native plant species,” Hohman said. “But in the council’s opinion, the BLM could be doing more. We don’t understand why they aren’t doing more.”

Some BLM offices tend to be more reactive than proactive, she said, relying too heavily on herbicides to kill invasive plants after they’ve become established. Instead, she’d like to see the agency do more to keep invasives from spreading by requiring off-highway vehicles and livestock operators to clean off any potential seeds they’re carrying before entering BLM land.

Herbicides On Public Land

Using herbicides on big swaths of land isn’t a new thing in the West. One University of Montana study estimated that more than 1.2 million acres of US public land—a chunk larger than the state of Rhode Island—were treated with herbicides in 2010.

The recently approved herbicides—Aminocyclopyrachlor, Clethodim, Fluazifop-P-butyl, Flumioxazin, Imazamox, Indaziflam and Oryzalin—join 21 others previously allowed by the BLM. Flanigan also pointed out that some of these chemicals aren’t necessarily new to public lands, since they’re already approved by other federal agencies.

“These are being used by our partners across the landscape,” he said. “The BLM is somewhat the last one to start using these specific herbicides.”

The BLM approval doesn’t mean these herbicides can be used immediately, either. Each local land office would first need to do an environmental impact study with a public comment period before any of these chemicals get sprayed or spread as powder, Flanigan said. Then local offices could decide on a case-by-case basis how to mitigate potential herbicide impacts by doing things like creating buffer zones around sensitive landscapes or waterways.

There are concerns about mixing chemicals and wildlife, though, which the Desert Tortoise Council sent to the BLM during the agency’s decision process. One way to potentially limit direct contact between tortoises and herbicides is timing applications to coincide with colder seasons when tortoises are usually dormant, Hohman said, but animal behavior can be unpredictable.

“It could be a nice sunny day the next day (and) a tortoise could come out and start eating vegetation that you just sprayed less than 24 hours earlier. So it’s really complicated,” she said.

It’s also unclear how long the herbicides remain active on different surfaces, she said. Tortoises eat rocks and soil as part of their digestive process because they don’t have teeth to grind up their food, so lingering herbicides could potentially enter their bodies that way, too.

There’s also some concern that herbicides could hurt native plants even though they’re meant to only target invasives.

In a greenhouse study, Cara Nelson looked at how two herbicides affected 10 species of native plants, both at full strength and diluted. It found that the herbicides inhibited the germination of native seeds the same way they did for invasive plants, which meant virtually no seed growth. Another study Nelson was a part of found the effects of herbicides in soil can continue to negatively impact native seed growth up to 11 months after application.

Alternatives To Herbicides

So if not herbicides, what are the other options for battling invasives? One way to fight cheatgrass, Nelson said, is manually removing the plants—basically hand-pulling weeds. That’s something anyone can do in their yard, and it can be very effective with no chemicals. It doesn’t work for some other species, though, and it’s tough to do across large areas.

Another option might be to just let sheep do the work. That’s exactly the type of biological control that Nelson has studied in Montana, and it turned out to be pretty effective.

In that research, sheep were trained to eat invasive plants, such as leafy spurge. Then they were unleashed on areas that had a lot of those plants and just did their thing: graze.

“Amazing tool, right?” Nelson said. “They need to eat, so you’re providing food for them.”

In the study, the sheep overwhelmingly gobbled up the invasives compared to nearby native plants. The key, Nelson said, was to keep moving the sheep to new pastures because they eventually started eating more native plants as the invasives became harder to find.

No matter how invasive plants are removed, Nelson said eradicating something bad should not be the only goal; there also needs to be a focus on restoring something good. In this case, that could mean reseeding the area with native plants and taking other steps to create the ecosystem land managers would like to see.

“If you’re just focusing on removing the weed without consideration of what you need to do to rebuild that native plant community,” she said, “what you could end up with is secondary invasion by another weed.”