Cheatgrass herbicides researched

Torrington – The spread of cheatgrass across prime grazing land in the Plains has scientists conducting research to find ways to control the moisture-draining plant. Jake Courkamp, a PhD candidate at Colorado State University (CSU), spoke to ranchers recently about seed bank management for long-term annual grasses during the Southeast Wyoming Beef Production Convention in Torrington.

“The take-away today is the importance of the soil seedbank and the importance of a multi-year approach if we hope to make progress with winter annual grasses,” he said.

Cheatgrass challenge

Courkamp told producers the spread of cheatgrass is a problem because the annual plant germinates early, compared to the native perennial species of grasses commonly found on rangeland. 

“It uses up the soil moisture and nutrients before native perennial species get a chance to,” he said. “Cheatgrass grows fast in the spring and has a short time frame for nutritional grazing before it dies off.” 

Cheatgrass also produces a lot of fine fuel and litters in between the perennials that can increase the likelihood of fire. 

“Dead cheatgrass makes fire burn hotter and faster,” Courkamp said. “The fine fuel will help the fire move fromone bunch of grass to the next much quicker. It makes it harder to control or manage fire because of that.”

If ranchers can graze cheatgrass during that small window when it’s still green, the plant can provide good nutritional forage for livestock in the spring and possibly in the fall if there is regrowth. 

“The problem with cheatgrass is its life cycle is so fast, it’s hard to utilize it effectively, because it’s only green for a few weeks,” he explained.

Controlling spread

Control of cheatgrass requires a multi-year approach. 

“If we only treat it for one year, the next year we will get residual in the seedbank that will germinate,” he explained. “Even at two or three years, there will still be some residual seeds hanging in the seedbank waiting to germinate.”

The best way to control it is to limit seed production for four years. 

“If we can exhaust the seeds in the soil seedbank, we can make some real long-term progress in annual grass control,” Courkamp explained.

Courkamp shared some research he has conducted in partnership with University of Wyoming (UW) and CSU that shows the chemical, Esplanade, which is produced by Bayer, can control invasive annuals for multiple years with one application. 

“Historically, it was used in perennial cropping systems, orchards and vineyards,” he said.

The chemical has been successful in controlling annuals like cheatgrass, Japanese brome, ventenata, medusahead and other annuals, as well as broadleaf weeds like Desert Alyssum, mustards and kochia. 

“It lays down a thin layer of chemical that only penetrates a centimeter to an inch deep,” Courkamp described. “Anything with a root that penetrates that top layer of soil can’t absorb it, so it isn’t affected by the product.”

The chemical sits on the top layer of soil, preventing annuals like cheatgrass from making cellulose. If the plant can’t make cellulose, it can’t absorb nutrients as effectively and will exhaust its resources. 

Once that happens, the plant will develop club roots instead of elongated ones, eventually killing the plant, Courkamp said.

Esplanade also has a low level of water solubility for an herbicide product, which helps it last a long time. 

“With one application, we can control annual grass seedlings for four to five years, according to the research that has been done so far,” he explained. “There are a lot more studies taking place.”

Research efforts

In one study Courkamp took part in, he said perennial plants like needle-and-thread grass were unaffected because they have deeper roots. 

“If we have all cheatgrass, this probably isn’t the product to use, but if we have mild to moderate cheatgrass, this product can be very effective if it is implemented at the right time.” 

“It can be very successful long term,” he said.

In the joint research between CSU and UW, Courkamp said they set up four randomized repetitions using five treatments. The treatments were untreated, Esplanade application at 3.5, five and seven ounces per acre, as well as mass treatment with Plateau. The treatments were applied in 2016 and analyzed in 2017 and 2018. 

“We looked at canopy cover and cheatgrass density,” Courkamp said. “The first year, Plateau performed really well, and we were at 20 percent cheatgrass cover that first year. But, by the second and third year, that number had climbed to 35 to 40 percent.” 

“The Esplanade brought the cheatgrass numbers down under 20 percent in a plot that started with 60 percent cheatgrass cover. By the second year, Plateau’s effectiveness was wearing off, while the Esplanade was ramping up,” he explained.

Chemical use

“If we are trying to eliminate cheatgrass, this is probably the only chemical option we can use to have long-term success at a four- to five-year level where you are exhausting the seedbank,” he told producers.

There is a Section 18 exemption for Wyoming to use the chemical to control Medusahead, with a two-week grazing restriction. 

“Last year, Sheridan County sprayed more than 6,000 acres with Esplanade to control medusahead. It is definitely being used in Wyoming,” Courkamp said. 

The product isn’t currently labeled for rangeland being grazed with livestock, but he expects Bayer to submit an application to the Environmental Protection Agency (EPA) by the end of the month requesting one. 

Once EPA receives the application, they have 15 months to review it and issue a grazing label, he said.

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.