SHERIDAN, Wyo. – Two new invasive weeds are threatening to degrade forage production, fuel wildfires and cause massive economic damage for producers in Wyoming and Montana.

Medusahead and ventenata, both winter annual grasses, are edging out native grasses to varying degrees in a 750,000-acre area stretching from north central Wyoming through south central and western Montana.

Both medusahead and ventenata germinate in the fall, robbing early spring moisture from native species like perennial grasses, flowering forbs and shrubby species. Both also have high silica content, making them unpalatable to livestock, as well as to wildlife like elk and deer, even more so than that other vexing invasive winter annual grass, cheatgrass. As a result, an invasion of either reduces the biodiversity and economic value of the land.

“We often jokingly call them the big bad brothers to cheatgrass,” said Dan Tekiela, University of Wyoming Extension invasive plant ecologist and assistant professor in the Department of Plant Sciences. “People can and do graze cheatgrass in the early season, but because of the higher silica content in these two species they’re abrasive and animals don’t like to eat them.”

The problem is potentially exponential and economically ruinous for area producers.

“It creates a positive feedback loop,” Tekiela said. “If they eat everything except ventenata and medusahead, it ruins competition, and you get more of it.”

Research from western states where the weeds are widespread suggest that established populations can reduce available forage up to 70 percent, particularly for cattle, said Brian Mealor, associate professor in the UW Department of Plant Sciences and director of the Sheridan Research and Extension Center.

“Imagine if the BLM cut your permit by 50 percent, how upset would you be?” Mealor said. “You’d have to cut your herd in half, that’s the thing to wrap your mind around.”

Medusahead and ventenata also pose a rangeland fire threat. Because animals won’t eat them, they wither and die, littering the landscape with their dry residual thatch, a ready fire source.

Concern about both invasive species developed just a few years ago. A pressed ventenata specimen at The University of Wyoming's Rocky Mountain Herbarium had been collected by a botanist in Sheridan County in the 1990s, but researchers didn't have access to the actual site where it had been found until Mealor commenced a project related to cheatgrass in 2016. He and his team quickly confirmed the presence of self-sustaining populations of ventenata; weeks later, an NRCS partner scouting for ventenata found medusahead.

“I would characterize it as an emerging rapidly developing issue,” Mealor said. “We started with basic questions about whether they’d be a problem in the northern Great Plains because they’ve typically been a problem in the west, and our research clearly indicates that ventenata is clearly going to be a problem.”

In Montana, scientists had known about small, scattered patches of ventenata on rangeland since the mid-1990s, but at that time it was fairly ephemeral and wasn’t demonstrating invasive qualities, said Jane Mangold, an associate professor and Extension invasive plant specialist at Montana State University. Before 2018, the population was thought to be limited to nine western and southwestern counties.

All that changed – and quickly. The ventenata population is exploding in the western third of state and down through south central Montana into Big Horn, Carbon and Yellowstone Counties, which straddle the Wyoming boarder.

“This last summer, we went from knowing we had ventenata in nine counties in Montana to finding it in another nine counties,” Mangold said. “It’s gone from hundreds of acres to thousands of acres in those counties. It’s increasing rapidly, expanding into areas that were previously uninfested and it appears to be doing this without any help from us.”

A sizeable infestation of medusahead – several hundred acres – was first recorded in Lake and Sanders Counties in northwest Montana in 2013. Researchers believe that’s the extent of it in Montana.

The Northeast Wyoming Invasive Grass Working Group (with the unwieldy acronym NWIGWG) was established last year. The group is made up of a number of land management agencies, local governments, landowners, university researchers and Extension professionals.

“It’s a partnership between all the area natural management people to come together to have a strategy to manage the problem across boundaries,” Tekiela said.

The group has effectively put together state and federal grant money to conduct surveys to determine the scope of the problem. They’re actively educating the population by distributing flyers, direct mailing producers with grazing leases and putting on workshops. Last summer, they hosted a tour for more than 80 weed specialists, landowners and others from five states.

The group has also decided on best management practices, partly in collaboration with the chemical industry. Chemicals that work on cheatgrass generally work on medusahead and ventenata with some variations, but NWIGWG was able to obtain an emergency exemption from the Environmental Protection Agency to spray Esplanade 200 SC, a pre-emergent herbicide from Bayer not yet approved for grazing.

The group’s most immediate management focus has been on medusahead because the infestation is newer and the weed less widely spread than ventenata. Complete eradication using Esplanade, reputed to give 100 percent control for three years with a single application, seems reasonable, Mealor said, even as research into other methods including hand pulling small patches, reseeding and prescribed fire is ongoing.

“We have a zero tolerance for seed production for the population that we know about,” he said. “The goal is to fully deplete the seed population by not allowing it to produce new seed and to prevent new seed from being introduced in the first place, whatever way that is.”

Luke Sander, supervisor of the Sheridan County Weed and Pest District, is working on the 10-year plan. Data from Washington State suggests both species’ seeds are viable for 5 years. Given the Northern Plains’ drier climate, Sander plans to spray on years one, four and seven. In areas already treated, forage has doubled in just one year.

“Esplanade doesn’t affect the perennials, it just allows them to use the resources,” Sander said.

Last summer, Sander surveyed 20,000 acres and found medusahead moving north to Montana. Last fall, Sander sprayed for medusahead over 4,900 acres, putting a large buffer around the problem area.

Management for ventenata is a little different. At the moment the focus is on “citizen science”: finding and reporting its presence so researchers have an idea of its scope, Mealor said.

“Landowners have a piece of ground here, a piece of ground there, cows here, cows there, so once they’re tuned in they’ve found more than our research team,” Mealor said. “They’ve got access, they’re familiar with the landscape, they’re on horseback in places not easily accessible. The willingness of landowners to contribute data is critical to making a landscape scale program like this work.”

From afar, it’s tough to differentiate medusahead and ventenata from other invasive annual grasses like cheatgrass or Japanese brome. The trick is to get up close. Both invaders are annual grasses: individual plants persist for a single year and create a shallow, easy-to-pull root system, a relatively rare trait for most native grasses.

Medusahead seeds have long spines or awns that make it look similar to the perennial foxtail barley and bottlebrush squirreltail. Unlike those species, the awns are variable lengths, longer at the top of the seedhead than at the base.

Ventenata is more difficult to identify from the seedhead. The seeds are much more widely spaced on an open panicle and rarely droop, as is the case for cheatgrass. The spines or awns on the tip of the seeds are short, approximately 1/2 inch, and are often bent halfway up.

Experts advise anyone who thinks they may have identified either species to contact their county weed and pest department or Extension agent for confirmation and to possibly cost share the management.

“It’s really important to have middleman to make sure that information is retained so it doesn’t get lost,” Tekiela said. “In three, four and five years we want to have information on where it was found and how it was managed.”

The main thing is to act.

“Time is of the essence, especially with medusahead, but for both, and letting it go to seed another year is not an option for anyone who wants to protect our land,” Tekiela said. “The sooner you’re out surveying it and finding it the better because if you get to it three to five years down the road it’s a bigger issue. Early detection, rapid response, I always try to remind people this is our best bet to be successful for long term management.”

For pictures, please visit or contact your region’s Extension educator or county weed and pest control district office for help identifying the weeds. Information can also be found at