Forage 2022: Downy Brome: A Threat to Our Rangeland
Across the United States, farmers, ranchers, and land-resource agencies battle the spread of downy brome. In almost every corner of the range and forage ground, downy brome, better known as cheatgrass, has invaded habitats and pasturelands, affecting wildlife and livestock forage grounds as we see them today.
Dr. Scott Nissen, professor emeritus from Colorado State University, Fort Collins, has studied management strategies for this non-native species. He highlights the root reason down brome has continued to be a problem for the US, “Downy brome produces an environment that perpetuates its own establishment, and we don’t have any significant native species that have the same lifecycle.”
This invasive winter annual has a rate of spread of approximately 14 percent each year. It germinates mostly in the fall, and is dormant until early spring. It will use up available soil moisture and nutrients before native grasses come out of winter dormancy.
“In the spring, downy brome will have used up all the moisture and nutrients before native grasses have a chance to utilize them. It produces a lot of seed, and downy brome is well adapted to fire, which is a really bad thing. Many land managers have attempted to use proscribed burns as a management tool, but control only lasts for one growing season. Downy brome rapidly reestablishes from the soil seed bank,” Nissen says.
Early in the season, downy brome is palatable for grazing, but it becomes dangerous to livestock when the seed heads emerge. At maturity, it can cause infection in the eyes or mouth of livestock, in addition to creating a serious fire hazard.
Nissen says, “The population gets denser and denser, builds up thatch for several years, and that’s basically what carries many wildfires with increased intensity and frequency. In places like the Great Basin, parts of Nevada and Utah, the fire frequency has changed from a fire once every 50 to 60 years to fires happening every five to 10 years now.”
Management options were previously limited. Ranchers would try grazing downy brome early and with high intensity, but it wasn’t a long-term solution. When herbicide options initially became available, they only offered a single year of control. There was a fundamental need for downy brome management that provides consistent control without negatively impacting native plants.
In 2010, indaziflam came on the scene. It was first introduced for the tree and vine market in California as Alion® (Bayer CropScience). Nissen and his colleagues noticed that downy brome was listed on the original label as a weed controlled by Alion. They spent three to four years researching the impacts of this herbicide on downy brome and native plants along Colorado’s Front Range, hoping for more than yearly control that other herbicides offered.
“Indaziflam provided long-term management downy brome control,” Nissen says. On cow-calf operations, budgets shift year-to-year, which makes it difficult to stay profitable during drought years when ranchers have to decide how much they can invest in weed control. “Ranchers and farmers work on thin margins, and that makes downy brome management hard to budget for. With this herbicide, ranchers are looking at three to four years of control from a single application.”
Nissen describes the return on investment for ranchers as substantial. “We’ve all seen cattle spend the least amount of energy possible when grazing. Cattle avoid areas with significant downy brome cover and overgraze areas that are not infested. With indaziflam, cattle operations can increase forage production by more than three-fold and we have seen highly productive sites where forage production increases five-fold when downy brome is controlled. So there’s a significant return on investment.”
The investment is the operative word.
Indaziflam, called Rejuvra® (Bayer CropScience) for rangeland applications, runs about $40/acre. Nissen highlights that it pays despite the high upfront cost. “The initial cost is high, but land previously lost to downy brome is now productive and can be used to produce a sellable commodity.”
When Nissen and CSU researchers first investigated the long-term effects of indaziflam application, the application was made by tractor. But after its commercial adoption, indaziflam was adapted to the fixed-wing application. It was then that it became a cost-effective herbicide for large-scale applications.
Indaziflam had the most impact on areas that aren’t totally lost to downy brome, but still have a significant component of native grasses remaining. The herbicide allows for three to five years to enhance and produce more grass on those sites. Nissen warns that using the herbicide in areas without remnant native grasses and perennial forbs could result in bare ground.
“This herbicide works as seeds are trying to germinate. This is why it works extremely well in perennial systems where you’re trying to deal with annual weeds. The herbicide won’t impact established perennials.”
Researchers continue to investigate how its use impacts annual native forbs. “We have seen some sites where two years after application, the whole hillside was just a sea of a really striking, native annual called snow-on-the-mountain. In general, we see native annuals increasing over time.”
From pastures to public land, downy brome management has become a necessity. In Colorado, many cow-calf operations that were early adopters of aerial Rejuvra applications saw an increase in forage production even with below-average precipitation. Nissen says, “When doing research like this, there are two sides to the coin. One side is improving the land that we have to increase its carrying capacity for ranchers and farmers, and the other side of the coin is using this product to improve wildlife habitat.”
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