What Newly Approved Herbicides Could Mean For Federal Land
11:05 minutes
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.”
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Segment Guests
David Condos
David Condos is Southern Utah Reporter for KUER. He’s based in St. George, Utah.
Segment Transcript
ANNA ROTHSCHILD: This is Science Friday. I’m Anna Rothschild. And now it’s time to check in on the state of science.
SPEAKER 1: This is KQR–
For WWNO–
Saint Louis Public Radio
Iowa Public Radio news.
ANNA ROTHSCHILD: Local science stories of national significance. The Bureau of Land Management has a big job. The federal agency maintains 245 million acres of public land, creating spaces for people to enjoy and protecting the flora and fauna that live there. But in Utah and elsewhere out West, invasive plants are changing the ecology of public lands.
Last month, BLM approved the use of seven new herbicides to kill invasive species on public land nationwide. This decision has been controversial among some groups that say these herbicides could do the opposite of what they hope, damaging native wildlife.
Joining us to talk about this story is my guest David Condos, Southern Utah reporter for public radio station KUER based in Saint George, Utah. David, welcome back to Science Friday.
DAVID CONDOS: Thank you, Anna. Glad to be here.
ANNA ROTHSCHILD: OK, David, so give us a bit of context here. How many acres of land might be sprayed with these herbicides and in which states?
DAVID CONDOS: Yeah, so when you’re talking about the Western US, there is just a ton of federal land all over the place. So the Bureau of Land Management, like you said, has those 245 million acres, and some of the states that have the most are like Alaska, Nevada, Utah. But there’s also a lot of BLM land in places like California and Colorado, too.
And when it comes to invasives, the BLM says it deals with these harmful non-native plants on about 79 million of those acres. And just to give you some sense of scale for this, the 79 million acres would be bigger than the states of Pennsylvania, Virginia, and South Carolina combined. And so–
ANNA ROTHSCHILD: Oh my goodness, that’s huge.
DAVID CONDOS: Yeah, the West is really big. So– and, of course, that doesn’t mean that all of those acres would be treated with herbicides necessarily. But just when you’re talking about the amount of land that is dealing with this problem–
ANNA ROTHSCHILD: Yeah.
DAVID CONDOS: It’s huge.
ANNA ROTHSCHILD: OK. And so what are the specific invasive plants that BLM is so worried about?
DAVID CONDOS: Yeah. So in my area, annual grasses like cheatgrass and red brome are a big concern. In other parts of the West, it might be flowering plants like leafy spurge, but across all of them, one thing these invasives have in common is that they are really prolific.
And so they produce tons of seeds. They grow really quickly and can just take over a landscape. And that is what worries people like Seth Flanigan He’s an invasive species specialist with the BLM.
SETH FLANIGAN: If we don’t remove this now, what is it going to look like 10 years from now?
DAVID CONDOS: So there’s this sense of urgency that they need to do something now to prevent this from getting out of control.
ANNA ROTHSCHILD: So what are the herbicides that BLM has approved?
DAVID CONDOS: Yeah. So there are seven of them, and you’ll have to bear with me on these pronunciations because these are not words that I say every day. So here we go. So you have clethodim in dasyphyllum, oryzalin, aminocyclopyrachlor, fluazifop-p-butyl, flumioxazin, and imazamox.
ANNA ROTHSCHILD: And bibbidi-bobbidi-boo.
DAVID CONDOS: Yeah, yeah. So they’re a bit of a mouthful, but the BLM told me that there are so many on this list because they have different specialties. Some are for grasses, some are for shrubs, and they can also be applied in different ways. One might be sprayed like from a truck or a backpack, or others might be spread on the ground as powder.
ANNA ROTHSCHILD: And they target different types of plants, too?
DAVID CONDOS: That’s the idea. Yeah.
ANNA ROTHSCHILD: Yeah. So if these herbicides are targeting different invasive plants, how do we know that they’re not going to harm the native plant life in Utah?
DAVID CONDOS: Yeah, so that’s the real trick because these invasive plants are not on an island. They’re right next to these native plants that you want to protect. And so the BLM believes that they can be effective in that way, but other folks say it might not be foolproof.
And so I talked with Dr. Cara Nelson, who directs the Ecology Restoration Lab at the University of Montana, and she’s actually done a lot of research about this exact thing about invasives and herbicides. And one was a greenhouse study that looked at what happened when you plant 10 species of native plants into soil treated with herbicides.
CARA NELSON: And what we found, which was surprising, was that all of the species we tested had almost no germination when seeded into herbicide soil.
DAVID CONDOS: And so what that means is that in that study, the herbicides were hurting the native plant seeds just as much as the invasives. And I should mention the two herbicides in that study were not the ones on this BLM list, but that’s still maybe a sign for concern.
ANNA ROTHSCHILD: So switching gears here for a moment, you spoke to some folks who work in tortoise conservation, and they’re particularly worried about these herbicides. What did they tell you?
DAVID CONDOS: Yeah, so in southwest Utah, where I live, this is the northern edge of the Mojave Desert, so threatened desert tortoises are just a big topic of conversation here all the time. Conservationists are already concerned that there’s pressures that these tortoises face from development and habitat loss, and now on top of that, some are concerned about these inherent risks that come from bringing chemicals onto their landscape, essentially what what’s going to happen if a tortoise eats plants that have herbicide on them?
And so I talked with Judy Hohman, who’s a board member with the Desert Tortoise Council, and she says it’s complicated because invasive plants aren’t great. They really hurt tortoise habitat, too, but she says removing them still needs to be done in the right way.
JUDY HOHMAN: We’re glad that they’re moving forward with trying to come up with more tools in their toolbox to deal with invasive plants, but in the council’s opinion, BLM could be doing more. We don’t understand why they aren’t doing more.
DAVID CONDOS: And by more, she means just other things the agency could also do to fight invasives. So she’s concerned that some land managers may rely too heavily on just herbicides rather than using additional tactics, and specifically she would like to see more prevention so requiring people to clean potential seeds off of their livestock or vehicles before they even go on to BLM land.
ANNA ROTHSCHILD: Oh, gotcha. So preventing the spread of these invasives into BLM land. Gotcha.
DAVID CONDOS: That’s right.
ANNA ROTHSCHILD: What are some of the other tactics that you mentioned that can maybe get rid of these plants without spraying the herbicides?
DAVID CONDOS: Yeah. So one is just manually removing them. And so this is really easy to visualize. This is hand pulling weeds. This is something a lot of listeners have probably done. This is something you can do in your yard or your town on a small scale. And this can actually be effective for species like cheatgrass. But when you’re talking about millions of acres, there are obvious limitations to that.
But then another option that came up in my reporting was why don’t we just let sheep do the work for us. Yeah, why have we thought of that? And so that University of Montana researcher Cara Nelson has studied that exact thing, and here’s how it worked.
So these sheep were trained to eat specific invasive plants ahead of time, and then they were brought onto this land that had a bunch of those plants. And then they just did their thing. They’re going to eat right. they don’t realize that they’re helping with weeds. They’re just hungry.
And so Nelson, the researcher, says that actually ended up being pretty effective. Her study showed, the sheep were overwhelmingly eating the invasives that they were trained to eat compared to the native plants next to them. And the key to all of this, she says, was to keep moving the sheep around because once they’d eaten most of the invasives, then they would start eating more native plants.
ANNA ROTHSCHILD: Perfect it’s like natural lawnmowers.
DAVID CONDOS: Exactly. Yeah. It’s called biological controls. And sometimes it can work.
ANNA ROTHSCHILD: So have we seen herbicide application at this scale before?
DAVID CONDOS: Yeah. So this is not a new thing. Even before these new herbicides got approved by the BLM, that agency already had 21 other herbicides on the list that it could use. And so the agency had been using herbicides for decades. Other federal agencies have as well.
And Nelson, that researcher, actually did a study on this, trying to quantify it. And the best they could do is they estimated around 1.2 million acres of US public land were treated with herbicides in the year 2010. So quite a bit. Those herbicides are already out there.
But, ultimately, Nelson said no matter what method people use to fight an invasive plants, there really needs to be a change of the mindset behind that. It can’t just be about getting rid of something bad. You also have to think about restoring something good.
ANNA ROTHSCHILD: Right. Yeah, preserving what’s already there.
DAVID CONDOS: And that’s actually her second clip. If you want to play it.
CARA NELSON: If you’re just focusing on removing the weed without consideration of what you need to do to rebuild that native plant community, you could be successful at removing that weed, but what you could end up with is secondary invasion by another weed.
DAVID CONDOS: And that’s because if you pull out cheatgrass, for example, it creates these empty niches in the landscape that will be filled by something. And so she said seeding those areas with native plants might be just as vital as removing invasives.
ANNA ROTHSCHILD: Right. Right. Because if you don’t, then something else is just going to come in and fill that gap.
DAVID CONDOS: Exactly.
ANNA ROTHSCHILD: Right.
DAVID CONDOS: Yeah, these invasives are sneaky.
ANNA ROTHSCHILD: Right. So what happens next? When might we actually see these herbicides in use?
DAVID CONDOS: Yeah, and that’s an important note because just because this national BLM approval happened, that doesn’t mean these herbicides are going to be used immediately. So the agency told me that each local land office would still need to do environmental impact study public comment period before these chemicals hit the ground. So residents will still get another chance to weigh in on this before it gets used in their area.
ANNA ROTHSCHILD: Right. Well, that’s all the time we have for now. And I’d like to thank my guest, David Condos, Southern Utah reporter for public radio station KUER based in Saint George, Utah. David, thank you so much for joining us.
DAVID CONDOS: Yeah, thank you, Anna.
ANNA ROTHSCHILD: And if you want to read more about this story, go to sciencefriday.com/herbicide.
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