Cheatgrass (Bromus tectorum), also known as downy brome or drooping brome, is an invasive annual grass that poses a widespread threat across North America, particularly in the western United States. It is classified as a winter annual, meaning it completes its life cycle within a single year, typically germinating in the fall. The plant’s aggressive growth and rapid spread degrade native ecosystems, creating pervasive problems for ranchers, land managers, and conservationists.
Identification and Life Cycle
Young cheatgrass plants are easily identified by leaves densely covered in soft, fine hairs, giving them a downy appearance. These leaves often exhibit a characteristic spiral twist, distinguishing them from many native grasses in the seedling phase. As the plant matures, the stem is slender and can grow from a few inches up to two feet tall, though its height depends on local conditions.
The plant’s most recognizable feature is its seed head, a loose, open panicle that tends to droop to one side. This inflorescence changes color as it dries out, shifting from green to reddish-purple, and finally to a straw-like tan color by late spring or early summer. As a winter annual, its life cycle is optimized for a competitive advantage over native perennial plants. Seeds germinate primarily in the fall when moisture is available, allowing seedlings to establish roots during the cooler winter months. This early start enables cheatgrass to rapidly draw up available water and nutrients in the spring before native perennial grasses begin their active growth.
Geographic Origin and Current Distribution
Cheatgrass originated in Europe, southwestern Asia, and northern Africa. It was introduced to the United States multiple times starting in the mid-19th century, primarily as a contaminant mixed with agricultural seeds, grains, and livestock feed, as well as in ship ballast. The first official documentation of Bromus tectorum in North America occurred in 1861, and it spread rapidly across the continent. By the late 1920s, it had established a presence in nearly all of the continental United States.
Today, its most dense and problematic concentration is in the arid and semi-arid regions of the Intermountain West, particularly within the Great Basin. This extensive distribution covers significant portions of the sagebrush steppe and bunchgrass regions in states like Nevada, Utah, Idaho, and Oregon. The plant thrives in disturbed areas and has become a dominant species, fundamentally changing these landscapes. Its widespread success results from its invasive nature and ability to colonize areas where native vegetation has been diminished by human activities.
Ecological and Economic Impact
The presence of cheatgrass has profound negative consequences, primarily by accelerating the natural wildfire cycle. Cheatgrass produces a dense, continuous layer of fine, dry plant material that cures much earlier in the season than native perennial vegetation. This carpet of highly flammable fuel drastically increases the likelihood of a wildfire, allowing fires to spread rapidly over large areas. In native sagebrush steppe ecosystems, the natural fire return interval was historically 60 to 100 years, but cheatgrass invasion has shortened this period to as little as three to five years in some areas.
This frequent fire regime eliminates slow-growing native shrubs and perennial grasses, which do not have time to reestablish themselves between burns. Since cheatgrass seeds are adapted to survive fire, the plant quickly dominates the burned landscape, creating a dangerous feedback loop that converts diverse shrublands into highly flammable annual grasslands. The plant’s competitive advantage also leads to the displacement of native species, resulting in a loss of biodiversity. Its early germination allows it to monopolize soil water and nutrients, particularly nitrogen, before native plants can begin their growth phase.
Cheatgrass also negatively impacts livestock production. It offers only a short window of palatable forage in the spring before quickly drying out. Once the seed awns dry and become sharp, they can injure the mouths and eyes of grazing animals, making the forage unusable and reducing the overall quality of rangeland.
Strategies for Management
Managing cheatgrass requires a sustained, multi-year, and integrated approach due to its prolific seed production and rapid life cycle. Since the plant reproduces entirely from seed, control strategies must focus on preventing seed production and depleting the soil seed bank. Eradication is generally not feasible over large areas, making long-term control and restoration the primary goals.
One effective strategy is the use of pre-emergent herbicides, such as those containing imazapic, applied in the fall to prevent germination. Chemical control is most effective when combined with reseeding efforts using desirable native perennial species, as a healthy, established plant community is the best defense against reinvasion. Mechanical methods, such as tillage or mowing, must be timed precisely before the plant sets seed to be effective.
Targeted grazing can also be utilized as a biological control method, often using livestock like sheep to intensely graze the cheatgrass when it is green and palatable in the early spring. This removes biomass and reduces seed production, lessening the fuel load for the upcoming fire season. This method requires careful management to ensure native plants are not overgrazed and must be repeated over multiple years to effectively deplete the long-lasting seed bank.