Bad or just ugly, annual brome grasses have become an important component of the Western rangeland environment. Commonly called “cheatgrass,” these non-native grasses — principally Japanese brome and downy brome — have invaded the West the past several decades.
Data collected in the 1980s clearly indicate these cool-season species can provide a large proportion of the spring forage produced in this region. But annual bromes add to the total forage base at the expense of perennial grasses.
As summer approaches, annual brome grasses quickly turn to blight on the land. They become poor in nutritive value and can provide explosive fuel for summertime range fires.
Rangeland scientist Marshall Haferkamp has studied the impacts of annual bromes on Western rangelands for more than 20 years. He works for the USDA Agricultural Research Service's (ARS) Fort Keogh Livestock and Range Research Laboratory in Miles City, MT.
“As with most annual grasses, herbage production from annual bromes is erratic from year to year,” he explains. “And many environmental factors work together to impact annual brome production.”
He says that while it's relatively easy to predict the density of annual bromes in a given year, it's difficult to know how much and for how long forage will be produced by the bromes.
Weight gains of stocker cattle grazing annual brome-infested rangelands often decline from spring to autumn in the Northern Great Plains. Haferkamp says this decline may, in some cases, be due to the presence of large amounts of early maturing annual bromes.
Fort Keogh scientists found in 1993-1995 that when the amount of annual bromes were reduced chemically, gains of stocker cattle increased from 2.02 to 2.29 lbs./head/day and from 15.6 to 18.1 lbs./acre during the May to September period.
“We think a portion of the increase in gain was due both to a shift in botanical composition of diets, as well as an increase in crude protein concentration in response to the herbicide,” Haferkamp says. At Fort Keogh, the annual bromes were replaced by a variety of perennial grasses and forbs more suitable to mid- and late-season grazing.
Grazing performance results following brome reduction will vary depending on the magnitude of annual production of bromes and the distribution of bromes within a given pasture.
“When bromes are less abundant or abundant in patches, livestock can more easily select perennial species in their diets,” Haferkamp says.
He notes that annual bromes are most abundant in years following wet autumns. Emerged seedlings will over-winter and begin growth in the early spring. Cool weather during the growing season prolongs their growth and herbage production. More then 10,000 annual brome seeds can be present in a square yard of infested mixed-grass prairies.
“Annual bromes will continue to persist on Western rangelands,” concludes Haferkamp. “Land managers will have to decide if they are a problem on their operations and then determine the most economical and effective management alternatives.”
Japanese brome (Bromus japonicus) and downy brome (Bromus tectorum) have invaded tens of thousands of acres of the Northern Great Plains, Great Basin, Intermountain, Rocky Mountain, California annual grassland, and Palouse Prairie regions of the West.
USDA-ARS range scientist Marshall Haferkamp suggests some management strategies for these alien, weedy, cool-season, annual grasses.
Grazing: Grazing brome-infested ranges early in the spring will manage and utilize bromes but not eradicate them. This approach often requires high-density, short-duration grazing during a narrow window of time.
Burning: Burning kills seedlings, reduces seed and removes mulch. Research has shown increased yields of perennial grasses after suppression of Japanese brome by burning. Greater reduction of bromes can be expected by burning when a year of below-normal precipitation follows.
Herbicides: Wyoming researchers reported promising annual brome control in the late 1990s with both glyphosate and paraquat. Care must be used in timing of application to reduce damage to associated desirable perennial grasses.