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An Assessment of Exotic Plant Species of Rocky Mountain National Park

Bromus inermis Leyss. (Bromopsis inermis)
Smooth Brome (Poaceae - Graminae)

Current level of Impact
Known locations in RMNP: Horseshoe Park, Beaver Meadows, extensively planted in RMNP along road shoulders.
Assessment: Currently believed to be expanding from road shoulders. If all populations were added together, would cover an area greater than 50 hectares. Found in some areas disturbed within the last 11-50 years, and may be inhibiting natural succession processes.

Distribution Origin: Eurasia
Geographic distribution: Within the U.S., smooth brome has been introduced in the northeastern Great Plains states as far south as Tennessee, New Mexico, California and north to Alaska. Distributed throughout Colorado, mostly western two-thirds of state from 4500 to 10,000'.
Ecological distribution: Along roads, waterways, in fallow fields, and other waste places. Found in openings in mountain brush, pinyon juniper, aspen, spruce fir, ponderosa pine, lodgepole pine, and meadow communities. High moisture requirement, and generally found in areas with minimum annual precipitation of 38 cm or more.
Soils: Adapted to sandy, loamy soils. Prefers clays and loams, but will grow on sands. Found to have better root growth on sandy soils than silty soils. Has a high mortality rate on organic soils. Moderately tolerant to flooding (can tolerate up to 24 days) and saline conditions.

Perennial cool season grass. Reproduces by rhizomes and seeds, capable of forming sod. A self compatible species. Starts growth in early spring and flowers May to July. Plants may regrow and reflower in fall if moisture is sufficient. Rhizome production begins between 3 and 6 months following germination.
Seed production: Estimates range from 156 to 10,080 viable seeds per plant.
Longevity of seeds: Most studies report a range of 2 to 10 years.
Seed dispersal: Seeds may be transported short distances by wind. Seeds may also be transported by ants, resulting in new brome patches on anthills.

Competition Highly competitive and may displace more desirable vegetation. In some cases, appears to be invading native prairie areas in plains region from roadsides.
Response to shade: Tolerates shade, grows well in shade or sun. However, seed production, number of shoots and rhizomes, and dry weight of plant parts are all reduced by shade.
Level of impact: Somewhat invasive, capable of forming a dense sod that may exclude other species.

Control Smooth brome can be a good target for selective control because it often occurs in single stands, or growing along with Poa pratensis. An important consideration is that it is an aggressive plant that reproduces vegetatively and by producing a large number of seeds. Also, control efforts are likely to be ineffective if there are insufficient species to colonize the area following treatment.
Mechanical: One close mowing when the plants are 18-24" (45-60 cm) tall, while the flowering head is still closed (followed ideally by three repetitions) is recommended. The best conditions for mowing are hot moist weather, followed by a dry period. Sather (1988) recommends that park managers may try repeated lawn mowing of brome beginning in late May and mowing at least 4 times during the season where brome patches are contiguous and pure.
Chemical: Rayburn et al. (1981) found that Roundup, or glyphosate (at rates of 3.4 to 9.0 kg/ha) are more effective than dalapon and pronamide. Rates of glyophosate as low as 0.5 kg/ha produced some effect, but control was better when rates approached 2.0 kg/ha. Other chemicals that have been used to control smooth brome include Kerb (pronamide), Arsenal (imazapyr), Bromax or Hyvar (bromacil), Princep (simazine), Aatrex (atrazine), and Spide (tebuthiuron).
Other: A well timed burn that treats brome in the early boot stage may be more effective than mowing at the same susceptible period. Recent research indicates that repeated prescribed burning in late May-early June reduces the number of tillers produced, and favors the regrowth of native warm season grasses. Generally tolerant to grazing.

Notes Cultivated as a forage grass. Considered a good forage for both livestock and wildlife. However, quality and palatability rapidly decline after inflorescence develops.


Lawerence, T., and R. Ashford. 1964. Effect of stage and height of cutting on 
    dry matte yield and persistence of intermediate wheatgrass, bromegrass, and 
    reed canary grass. Canadian Journal of Plant Science 41 :321-332.

McCarty, N.P., C.J. SciEres. 1966. Response of smooth bromegrass to several 
    herbicides. Proceedings North Central Weed Control Conference.

Paulsen, G.M. and D. Smith. 1968. Influences of several management practices 
    on growth characteristics and available carbohydrate content of smooth brome-
    grasses. Agronomy Journal 60:375-379.

Rayburn, J.H. and D. Smith. 1981. Herbicide and tillage effects on legume 
    establishment in bromegrass sod. Proceedings of Northeast Weed Science Society. 

Sather, N. 1988. Element Stewardship Abstract for Bromus inermis. The Nature 
    Consewancy, Minneapolis llpp.

Stubbendieck, J., C.H. Butterfield, and T.R. Flessner. 1992. Bromus inermis L. 
    pp. 82-82. In An Assessment of Exotic Plants of the Midwest Region. Final 
    Report. Department of Agronomy, University of Nebraska, Lincoln.

Vogel, K.P., W.R. Kehr, and B.E. Anderson. 1983. Sod-seeding alfalfa into cool 
    season grasses and grass alfalfa mixtures using glyphosate or paraquat. 
    Journal of Range Management 36:33-37.

Waller, S.S. and D.K. Schmidt. 1983. Improvement of eastern Nebraska tallgrass 
    range using atrazine or glyphosate. Journal of Range Management 36:87-90.

Wilson, G.D. 1992. Morphological characteristics of smooth brome used to determine 
    a prescribed burn date. Pages 113- i 16. In: D.D. Smith and C.A. Jones (eds.). 
    Proceedings of the Twelfth North American Prairie Conference. University of 
    Northern lowa, Cedar Falls.

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