Weed & Pest
Invasive species: Weed and Pest works to control cheatgrass invasionWritten by Emilee Gibb
Casper – Across the western United States, landowners, government agencies and local weed and pest organizations alike are working to control the ecological changes that are occurring due to cheatgrass invasion.
Natrona County Weed and Pest Supervisor Brian Connely explains that the control strategies they use now will have a significant impact on what the Wyoming landscape will look like for future generations.
“We’re managing the land for our generation and for the next. After that, they can make their own decisions,” says Connely.
Bromus tectorum, commonly known as cheatgrass, is an invasive weed species from Eurasia. The annual plant is extremely aggressive and thrives in disturbed areas including fire, overgrazing, recreation and construction sites.
While it is extremely prevalent in the western United States, the plant has very limited use for wildlife and livestock grazing.
“Cheatgrass is only palatable for two to four weeks out of the year in the spring,” says Connely.
A variety of mechanical, chemical and biological control measures can be used in managing cheatgrass invasion and are typically used in combination. However, eradication of cheatgrass can be extremely difficult once it is established.
Diligence is essential in cheatgrass eradication, as seeds can remain viable in the soil for several years, depending on the soil.
“The literature says that the seeds remain viable in our soil anywhere from one to six years, with a caveat of nine years,” explains Connely.
While cheatgrass is not a state-designated noxious weed in Wyoming, it is a county-declared weed for many counties.
Connely explains that the primary habitat in Natrona County is sagebrush steppe, and 66 percent of the nation’s pronghorn live within 200 miles of Casper.
Natural fires typically occur every 40 to 60 years in a sagebrush steppe habitat. However, cheatgrass invasion changes the fire interval to every five years.
“As the cheatgrass gets denser, the area becomes very fire prone. That time period in our ecosystem is right in time for summer thunderstorms,” he comments.
While the fire destroys all of the plant matter above ground, the cheatgrass duff on the ground creates insulation for a seedbank, protecting it from the fast-moving flames.
Cheatgrass also has an advantage over native grasses in using post-fire nutrients for rapid growth.
“After the fire, the cheatgrass is able to utilize nitrogen very well. Native grasses are not accustomed to nitrogen because there’s not much decomposition, resulting in low nitrogen in the native soil,” says Connely.
Because of the rapid growth and recovery of the cheatgrass compared to the native plants, the ecosystem changes to primarily cheatgrass and maintains the frequent fire interval.
“Our environment can’t do that,” stresses Connely.
Using an integrative approach to cheatgrass control can be extremely effective, notes Connely.
“Chemical control, when used judiciously and efficiently, can be a great tool, but it is not a solution,” he says.
Those involved in control efforts are able to use the herbicide imazap, which is known by the brand name Plateau. Plateau is a pre-emergent herbicide.
“Before germination, in the late fall, we spray it on the ground. It can halt germination for 2.5 growing seasons,” Connely explains. “When released from competition, our native grass community will respond and thrive.”
The process uses six to eight ounces of herbicide per acre, depending on the soil type.
Prices for aerial treatment vary somewhat from year to year, but it costs approximately $16 per acre in Natrona County.
“That’s $9 for the pilot and $7 for the chemical,” says Connely.
“Cheatgrass is everyone’s problem because it changes everything we need and love out of this landscape,” emphasizes Connely. “It is important that people be able to recognize it as ‘my problem.’”
According to Connely, educating the public about ecosystem sustainability and health is essential to cheatgrass control. Noxious weed management is not well understood by many, requiring instruction on the complexity of the issue.
“Many people can’t tell whether the ecosystem is healthy or not, and they simply want an easy fix,” says Connely.
Cheatgrass control is a joint effort between landowners, government agencies, local weed and pest offices and other stakeholders.
“Local weed and pest agencies develop decision making priorities with the Bureau of Land Management, Natural Resource Conservation Service, Wyoming Game and Fish Department and the landowner,” he continues.
Research is currently being done on using Pseudomonas fluorescens as a bioherbicide. It is a naturally occurring, cold-loving bacteria that targets cheatgrass roots during spring growth.
“They are looking at bacteria as another management tool, not as a cure,” emphasizes Connely.
Like any other treatment option, there are periods of time that the bacteria would not be effective in controlling cheatgrass growth. However, Connely is hopeful that it will be a useful tool to use in combination with current treatments.
“If the treatments can be overlapped with chemical herbicides and other treatments and the ineffective period isn’t the same, maybe there’s a synergy there,” he concludes.