Cheatgrass (Bromus tectorum), also known as downy brome, is an invasive throughout the USA and Canada. It is of particular concern throughout rangelands where it outcompetes native species important to livestock.
Identification guide: Bromus tectorum
Cheatgrass is a smallish grass reaching 40-90cm (Fig 1). Early in the growth season (when it is small in size), the grass has numerous fine hairs located on its stem, especially near the base of the stem. When it reproduces, cheatgrass is characterized by the open and droopy appearance of its reproductive structure (called a panicle). A panicle consists of multiple long side-branches that give it its droopy shape. After the plant has reproduced, the panicle contains many seeds. Depending on the size of the plant, a panicle may have 25-50 seeds; or if the plant is relatively large, hundreds of seeds. Each seed has a fairly long (7-18mm) and straight structure attached to it called an awn (or beard). Awns aid in attaching a seed to animal fur, clothing (especially socks) and machinery; thus helping to spread seeds from one location to another. The plant starts off green in color and turns purple, and then tan as it matures throughout the course of the season (Fig 2).
Background: Cheatgrass (Bromus tectorum), also known as downey brome, downy bromegrass, downy chess, early chess, slender chess, drooping chess, junegrass, military grass and bronco-grass, is native to the Mediterranean region, much of Europe, and central Asia. The grass is invasive in North America (NA), where it occurs widely across the United States (US), and in parts of Canada and Mexico. Cheatgrass is particularly abundant in the Pacific Northwest and the Intermountain West regions of the US. It was first introduced into the eastern US, and it was first collected in western NA near Spences Bridge, British Columbia in 1889. It was likely introduced as a contaminant of shipping materials, and crop seed. Its seeds (Fig 3) are easily dispersed by wind and also easily transported by people and animals by attachment to clothing and fur, and machinery. It was able to take over vast disturbed areas quickly due this dispersal ability and its ability to grow in a wide range of soil and moisture conditions.
Impact: It invades rangelands and pastures as well as prairies, fields and disturbed areas such as roadsides. For example, over 5 million ha of overgrazed pastureland in the US is reported to be completely taken over by cheatgrass. It can reduce crop yields (e.g. can reduce wheat and rye yields by 27% and 33%, respectively). Areas invaded by cheatgrass are of low conservation value, but do provide forage for species such as Chukar and grey partridge (another invasive species).
However, cheatgrass is capable of outcompeting important native species in areas of conservation value such as sagebrush steppe ecosystems. Finally, cheatgrass extensively alters ecosystems by changing the fire regime in areas heavily invaded by the grass. Aside from preventing further spread of this species, current control methods include combinations of herbicide applications, tillage, mowing, targeted grazing. Currently, soil bacteria which are reported to be pathogenic to cheatgrass show promise as a potential biological control agent, and classical biological control programs prospecting for potential agents are currently underway.