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Cheatgrass remains a challenge in Wyoming rangelands

by Wyoming Livestock Roundup

Although for some time the common belief was that Wyoming was too high and too dry for a substantial cheatgrass problem, it’s since been established that downy brome, or cheatgrass, is a problem in the state.
“We used to think cheatgrass was confined to low elevations, but have now found dense stands well over 9,000 feet, so we know it’s moving upward,” says UW Extension Weed Specialist Brian Mealor.
This is significant, he notes, because planning a grazing system with cheatgrass as a major part of the forage base is very unpredictable.
Cheatgrass is readily identifiable and is known as downy brome because of the fine hairs on the plant. That, and the purple color and nodding seed heads tend to stand out.
“When entire landscapes turn purple it’s hard to miss,” says Mealor. “One thing we often see are firm, dense stands of seedlings, and they can have a second flush of germination in the spring, which makes it a challenge to control. It also doesn’t take much moisture in the fall to increase the amount of cheatgrass.”
Mealor says the grass is incredibly competitive, reducing the growth of crested wheatgrass and bluebunch wheatgrass, and its entire life is about producing seeds – from 13,000 to 20,000 seeds per square meter.
“Plant densities range from 10,000 to 13,000 plants per square meter, and that doesn’t allow much room for anything else,” he says, adding that, while the problem is most seen in the Great Basin, Wyoming does see large monocultures of cheatgrass.
Although published literature suggests cheatgrass seed is viable for around five years in the soil, most will germinate within one year if conditions are right. Mealor says the difficulty with the data is that it’s hard to pin down accurate seed longevity times, and that recent work suggests a small portion of the seed might be viable for up to nine years or more.
“That persistent seed bank is a problem we have with reinvasion after control,” says Mealor.
He adds that the rule of thumb for rangeland managers is that they should begin to be concerned and to implement treatment when native grasses number less than three plants per square meter.
“At what point in time do we decide to implement cheatgrass control on rangeland?” asks Mealor. “As soon as we see it? I don’t know that there’s enough money in the Federal Reserve to start doing that across the state, and one thing we’re trying to move forward is identifying some of those thresholds.”
He says that cheatgrass at minimal densities will allow for establishment of native seeds, and that it doesn’t have to be completely eradicated.
One of the biggest ecological impacts is the ability of cheatgrass to change fire frequencies.
“Big sagebrush subspecies don’t respond well to fire, as they don’t re-sprout and have to re-grow from seed,” says Mealor. “Some places in the Great Basin have changed from a historic fire frequency of 100 to 150 years between fires to burning every three to five years, and if you get a fire return that quick the odds of reestablishing sagebrush are very low.”
The buildup of litter from cheatgrass creates fine fuels even early in summer, and all it takes is one lightning strike to initiate a fire cycle.
“I don’t think we’ve reached that point in a lot of the state. We have a good perennial component, and a lot of shrubs, so that gives us the opportunity to go to some high-priority areas to prevent the cheatgrass wildfire cycle,” explains Mealor.
Control efforts aim to increase species diversity, improve the predictability and longevity of the forage base, protect the perennial plant community by reducing the probability of an altered fire regime and to reduce the susceptibility to secondary invaders.
Mealor says the herbicide Plateau is the most widely used for cheatgrass in rangeland.
“We’ve seen the best results with pre-emergent application in the fall. Plateau can maintain residual desirable plants, and there are no grazing restrictions. We can also reseed following applications, and I’ve heard some really good reports,” he states, adding that the chemical does need to reach the soil surface, and can be intercepted by litter, which causes less and unpredictable control. However, sagebrush is resistant at label rates.
Matrix is another chemical option that has a rangeland restoration label for fall application.
“I work with it as a pre-emergent, and my thought is that if we have soil residual and can get it on pre-emergent, our window of efficacy will be good,” says Mealor.
Matrix is applied at low rates – the label recommends two to three ounces per acre, though some reports show good control down to one ounce. Mealor says it is expensive, at $17 per ounce, because it was originally developed for crop markets and still carries that cost with it.
Regarding Roundup herbicide, Mealor says at low rates in early spring it can suppress cheatgrass populations.
“You want to apply it when the desirable vegetation is dormant, or not 100 percent actively growing, and it can be used in reseeding projects,” he notes. “Apply it at around 14 ounces per acre, and if you can wait for the population to be at half seed set you’ll catch the entire group. It’s a low-cost option for chemical control.”
Mealor says Journey is another low-cost option that can be applied both pre- and post-emergent, and that fall is a good time for application.
Following treatment, Mealor says reseeding may have to be an option in cases where productive rangeland has been dominated by cheatgrass, with no desirable species left.
“Herbicides are probably the most effective control tool we have, from a cost and efficacy standpoint,” says Mealor of the solution to encroaching cheatgrass.
Christy Martinez is managing editor of the Wyoming Livestock Roundup and can be reached at

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