Photographer: Bruce Bosley Affiliation: Colorado State University Source: Bugwood.org Copyright: (CC BY 3.0)
Bromus tectorum is a winter annual grass that grows in small tufts (20-60cm tall) from a fibrous root system. I has many finely hairy, drooping, yellowish-green, bristly spikelets in a multi-branched cluster. The spikelets are the sharp-pointed sections that can injure grazing animals or can cling to hiker’s clothing. Stems are erect and slender with flat leaf blades.
Bromus tectorum is a threat to ecosystems because it quickly develops a large root system in the spring, by the time native grass seedlings start to grow in April or May, Bromus tectorum has stolen most water out of the top foot of soil. Although mature native grasses can get water from lower soil regions, seedlings cannot get their roots deep enough into soil to access water before drought sets in, and thus, die of thirst. Therefore, once downy brome has invaded it seriously alters the ecosystem and it then no longer supports the natural vegetation community. Bromus tectorum can maintain dominance for years where native vegetation has been eliminated. It is most invasive in areas receiving 12 to 22 inches of annual precipitation. Also, this grass has been known to exacerbate wildfires and preventing the “cheatgrass-fire cycle” has become a new initiative for researchers.
Downy brome is a winter annual that is self-fertilizing. It germinates in the fall, over winters as a seedling, then flowers in the spring. The plants typically flower from mid-April through June. Spikelets are dispersed within a week of maturity by wind, attachment to animal fur, or small rodents. Seeds move as a contaminant in hay, grain, straw, and machinery. An abundant seed producer, downy brome has been reported as having a production potential in excess of 300 seeds per plant.
Downy brome was introduced accidentally in the 1861 in New York and Pennsylvania through contaminated shipments. By 1928, it was found all throughout the United States.
Eurasia (northern Africa to southwestern Asia)
U.S. Habitat: Downy brome grows in many climatic areas and will grow in almost any type of soil. Research has shown that it is most often found on coarse textured soils and does not grow well on heavy, dry, and/or saline soils.
U.S. Present: All United States including Hawaii and Alaska
Fire, mowing, grazing, tillage, and planting of competitive native plants have all been shown to reduce populations of downy brome. Based on the fact that this is a cool-season annual, it could be assumed that prescribed fire in late spring could be a valuable tool in controlling this species, especially on an area where the preferred vegetation is primarily warm-season grasses. A prescribed fire should kill seedlings and further reduce the surface seed bank. A study conducted on spring burning of the closely related Japanese brome (Bromus japonicus Thunb. ex Murr.), showed that consecutive annual burns reduced brome density and standing crop.
Mowing has been shown to reduce seed production when the stand is mowed within 1 week following flowering. This reduces seed production, but does not eliminate it because later developing plants will escape mowing and will produce seed. Late fall and early spring grazing has been shown to significantly reduce plant numbers. However, heavy grazing will promote downy brome invasion. Spring or fall tillage will significantly reduce plant numbers. Although a strongly competitive crop, it will not tolerate shading.
Research into the biological control of downy brome is limited. It is known that rabbits and mice will feed extensively on this species as do migratory grasshoppers (Melanoplus sanquinipes). Downy brome is often infected with a head smut (Ustilago bulleta Berk.) that, when severe, may reduce seed yield. Some research has been conducted on pink snow mold (Fusarium nivale) as a biological control agent, but information has yet to be released. In addition to these molds and smuts, over 20 diseases of downy brome have been reported.
Schaeffer, S. M., Ziegler, S. E., Belnap, J., & Evans, R. D. 2012. Effects of Bromus tectorum invasion on microbial carbon and nitrogen cycling in two adjacent undisturbed arid grassland communities. Biogeochemistry, 111(1-3):427-441.
Mazzola, M. B., Chambers, J. C., Blank, R. R., Pyke, D. A., Schupp, E. W., Allcock, K. G., ... & Nowak, R. S. 2011. Effects of resource availability and propagule supply on native species recruitment in sagebrush ecosystems invaded by Bromus tectorum. Biological Invasions, 13(2), 513-526.
Woodward, Susan L., and Joyce Ann. Quinn. 2011. Cheatgrass. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood. 443-46. Print.