Cheatgrass, Bromus tectorum
Also known as downy brome or drooping brome.
Weed identification:
Bromus tectorum is an annual grass species native to Europe and western Asia, but widely present in North America and Colorado. It is known for its aggressive, invasive nature, particularly in dry and disturbed areas. It is a diploid species (2n = 2x = 14). This species can be identified based on certain features:
- Growth form is an erect annual grass which grows in distinct bunches, with multiple stems that emerge from a single base and have a clustered appearance. It typically grows between 20 to 50 cm tall and can reach up to 90 cm in favorable conditions.
- Leaves are bright green and densely covered with hairs on both surfaces. The leaf sheath is hairy and fused and does not overlap the leaves.
- Ligule is a membranous and short structure present at the base of the leaf blade. There are no auricles.
- Stems are slender, erect, and slightly hairy. Stems often turns purplish as they dry out, becoming straw-colored when fully mature.
- Inflorescences are a loose, open, nodding panicle ranging from 2 to 8 inches long. The panicle branches arch and droop at the tips, with each spikelet containing 3 to 8 florets. The florets have long and straight awns that are purple when mature.
- Seeds are light brown and turn purplish at maturity. Covered in fine hairs and have long awns.
- Seedlings are bright green with hairy leaves. The first true leaf is often twisted, an important feature to recognize the species at an early stage.
- Roots are fibrous root system with shallow main roots and extensive lateral roots.
- Color change happens with this plant. The mature plant changes color from green to purplish and then to a straw-like color when completely dry.
Cheatgrass ligule
Image credit: Steve Dewey, Utah State University, Bugwood.org
Cheatgrass fruiting structures
Image credit: Leslie J Mehrhoff, University of Connecticut, Bugwood.org
Cheatgrass seeds
Image credit: Jan Samanek, Phytosanitary Administration, Bugwood.org
Biology and life cycle:
- Growth habit: Bromus tectorum germinates primarily in the fall, the seedling goes through the hibernation period in winter, and resumes growth in early spring, maturing by late spring or early summer. It has a rapid growth cycle typical of winter annual grasses and completes its life cycle within one growing season. Its growth is highly plastic and allows it to adapt to various environmental conditions. This species occupies open spaces and disturbed areas.
- Emergence dynamics: seeds primarily germinate in the fall when moisture is available but may also germinate in the spring if fall conditions are unfavorable. Seedlings emerge rapidly, usually from the top 2.5 cm of soil, though they can emerge from depths of up to 8 cm. The species grows in a wide range of temperatures and moisture conditions.
- Pollination: cheatgrass is primarily self-pollinating, ensuring successful seed production without the need for external pollinators. The flowers are cleistogamous and self-pollinate without opening, which minimizes genetic variation but ensures reproduction even in isolated environments.
- Seed production: plants can produce over 500 seeds under optimal conditions, what contribute to its rapid spread. Seed production varies based on plant density, environmental conditions, and timing of germination. The plant is highly adaptable and produces seeds even under drought stress or grazing pressure.
- Seed viability: seeds have high initial viability, often near 99%. Most seeds germinate within the first year, but some remain viable in the soil seed bank for up to 2-3 years. Seed burial extends viability, with seeds remaining viable for longer periods when buried at depths of up to 20 cm.
Resistance
Globally, there are twelve reported cases of herbicide resistance in this species. Eight of these cases have been reported in the U.S, and there are no confirmed cases of herbicide-resistant in Bromus tectorum in Colorado. The resistance is reported to ALS, ACCase, FSII, and EPSPS inhibitors. There are relates of ALS, ACCase and FSII resistance caused by mutations in the target genes. P450 metabolism also is described for resistance to ALS herbicides.
Integrated weed management strategies based on Colorado cropping systems:
Prevention
- Equipment cleaning after working in infested fields, to prevent the spread of cheatgrass seeds to new areas.
- Use of certified seed free of cheatgrass contamination.
- Field monitoring for early detection: look for cheatgrass seedlings in the early spring to catch infestations before they spread extensively.
Cultural
- Rotating crops with those that provide dense canopy cover, like wheat or millet or with crops like legumes.
- Using cover crops to shade out and reduce the establishment of cheatgrass by competing for light, water, and nutrients.
- Planting crops early to provide a head start over cheatgrass, which typically germinates in fall and grows early in spring.
- Using higher seeding rates for crops can shade out cheatgrass effectively. This increases crop density and limits space for cheatgrass to establish.
Mechanical
- Using shallow tillage to disrupt cheatgrass seedlings early in the season, especially before they establish a deep root system.
- Regular mowing before cheatgrass can set seed can prevent it from completing its lifecycle. It is most effective when done early in the growing season, before the seed heads mature.
Biological
- Introducing grazing animals in a controlled manner to prevent cheatgrass from going to seed.
- Biological control options for cheatgrass are limited, some studies have shown potential in using specific fungi or insects that target cheatgrass seedlings. Research into these biological control agents is ongoing, but their use in Colorado cropping systems is still emerging.
- Prescribed burning is sometimes used in natural areas to manage cheatgrass to remove dead plant material and reduce seed banks.
Chemical
- Applying pre-emergence herbicides like tebuthiuron and pendimethalin before cheatgrass seeds germinate to inhibit seedling establishment.
- Applying post-emergence herbicides like glyphosate, fluazifop, bromacil and imazapic.
- Rotate between different modes of action to prevent resistance and tank mixing herbicides with different modes of action for enhanced control.
- Apply herbicides in the early stages of cheatgrass growth (late fall or early spring) to maximize control before it flowers and sets seed.
References
Resources and References
Bartlett, E., S.J. Novak, and R.N. Mack. 2002. Genetic variation in Bromus tectorum (Poaceae): differentiation in the eastern United States. American Journal of Botany 89(4):602-612.
Heap, I. 2025. International Herbicide-Resistant Weed Database.
https://www.weedscience.org/Home.aspx
POWO. 2025. Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. https://powo.science.kew.org/
Ribeiro VHV, Barroso J, Brunharo CACG, Mallory-Smith C. Herbicide resistance in Bromus spp.: a global review. Weed Science. 2023;71(5):422-437. doi:10.1017/wsc.2023.42
USDA, NRCS. Plant Guide – CHEATGRASS, Bromus tectorum L.
https://plants.usda.gov/DocumentLibrary/plantguide/pdf/pg_brte.pdf