Taxonomic name: Bromus inermis Leyss.
Synonyms: Bromopsis inermis (Leyss.) Holub
Common names: arva rozsnok (Hungarian), Austrian brome (English), awnless brome (English), bladfaks (Norwegian), brome de hongrie (French), brome sans arete (French), bromo inerme, bromo suave (Spanish-Mexico), bromo-liso (Portuguese), capim-cevadinha (Portuguese), cebadilla perenne (Spanish-Argentina), foderlosta (Swedish), forasacco spuntato (Italian), grannelose trespe (German-Switzerland), Hungarian brome (English), idänkattara (Finnish), ko suzume no chahiki (Japanese), koster bezostyj (Russian), kweekdravik (Dutch), magyar roz rok (Hungarian), rehukattara (Finnish), Russian brome (English), smooth brome (English), smooth bromegrass (English), staklos hejre (Danish), stoklosa bezostna (Polish), sverep bezbbranný (Czech), vihneetön kattara (Finnish), wehrlose trespe (German), wu mang que mai (Chinese)
Organism type: grass
Bromus inermis is an invasive, perennial C3 grass that has made an extensive impact on the grasslands of North America. B. inermis has become established by invading disturbed prairies and through repeated introductions for soil retention and livestock graze. It is known to have negative impacts on growth of native plants by slowing their growth and increasing extinction. B. inermis is also known to significantly impact the population dynamics and movement behaviour of several native arthropod species in North American prairies.
Bromus inermis is a perennial C3 grass that grows from an extensive creeping rhizome. Its stems are hairless and erect, reaching 1.5 metres. Leaf blades are flat, hairless and 15-40cm long and 5 -15mm wide (ANHP, 2004). Leaf blades are greyish blue on the upper side and green on the lower side (Hilty, 2007). B. inermis displays closed leaf sheaths, with a small V-shaped notch and does not have auricles. It possesses an open panicle 5-20cm long, with 1 to 4 branches per node. Generally, there are several purple-brown spikelets per branch, each 2-3cm. long. Seeds are elliptical and range in colour from pale yellow to dark brown, and are approximately 1.2cm long. Awns are less than 3mm but may or may not be present (ANHP, 2004).
natural forests, range/grasslands, ruderal/disturbed
Bromus inermis occurs on roadsides, riverbanks, edges of fields, prairies, woods and pastures. It prefers sandy soils to silty ones (Sather, 1987). B. inermis needs well aerated soils with a pH from 5.5-8. B. inermis is not tolerant of anaerobic, calcareous, or salty conditions, but can tolerate temperatures as low as negative 38 degrees Celsius (ANHP, 2004). It is also very drought tolerant which can be attributed to its deeply penetrating root system (Sather, 1987) B. inermis is not shade tolerant, and seed production, number of shoots and rhizomes, and dry weight of plant decreases when B. inermis does not receive sufficient sunlight (Sather, 1987).
Bromus inermis is a highly competitive C3 grass that forms a dense sod, resulting in smothering and exclusion of other (native) species and decreasing natural biodiversity (ANHP, 2002; Oftinowski et al., 2007). ANHP (2002) writes that "Smooth brome may inhibit natural succession processes...and [serves as an] alternate host for viral diseases of crops." Anemone patens, a long lived native perennial in North American grasslands, is negatively affected by the presence of B. inermis. The thatch left by previous B. inermis growth creates an issue for survival and germination of A. patens seeds (Williams & Crone, 2006). B. inermis has also shown to alter the population dynamics of the dominant native perennial prairie cordgrass (Spartina pectinata). When B. inermis grows in conjunction with native S. pectinata is known to reduce patch growth, decrease colonization rates and increase extinction rates of the native species (Dillemuth et al., 2009). B. inermis is also known to significantly impact the population dynamics and movement behaviour of several native arthropod species in North American prairies (Baum et al., 2004; Cronin 2003a, b, 2007; Cronin & Haynes 2004; Cronin et al., 2004; Haynes & Cronin 2003).
Silver leafhopper (Athysanus argentarius), an insect introduced form Europe, is frequently found in fields of smooth brome. Other insects that feed on Bromus spp. include the large headed grasshopper (Phoetaliotes nebrascensis) and the many winged wainscot (Leucania multilinea). Because smooth brome "lacks awns that can injure...mouthparts and gastrointestinal tracts" it is enjoyed by rabbits and hoofed herbivores (Hilty, 2007).
B. inermis is planted to increase forage or to reduce erosion after fire (Grace et al, 2002). Smooth brome is used as hay, pasture, or silage for livestock, as it is high in protein. It works well in a cropping system with alfalfa or other legumes. B. inermis' massive root system makes it a very effective erosion control (USDA, 2007).
Native range: France to Siberia (Sather, 1987)
Known introduced range: Bromus inermis has been introduced to all continents except Antarctica.
Introduction pathways to new locations
Agriculture: B. inermis is widely planted as a forage crop.
Landscape/fauna "improvement": B. inermis has been introduced to some areas for use in wildlife and conservation cover mixes for nesting cover and food.
Local dispersal methods
Acclimatisation societies (local):
Natural dispersal (local): B. inermis can spread by rhizomes and seed dispersed by wind.
On animals (local): Seeds can be dispersed by ants and birds.
Management in some areas is aided by Bromus inermis' tendency to grow in nearly pure swaths. Sather (1987) offers a caveat, that "because of its cool season habit [B. inermis] is often lumped together with Poa pratensis," another exotic grass that affects tallgrass /mixed prairies. However, differences in the two species biology and their responses to management techniques reveal "that there is a difference in the timing of the most susceptible phenological stages of the two species" (Sather, 1987). Sather (1987) notes that "more effective management of smooth brome might be achieved by first understanding the relative proportions of B. inermis to P. pratensis and their spatial distributions in the mosaic of vegetation. Treatment schedules could then be adapted to impact smooth brome in the boot stage in areas where it is the rightful target species."
Mechanical: Cutting smooth brome while it is still in boot stage (while the flowering head is still enclosed in sheath) may be the most effective means of mechanical control. Boot stage usually occurs while B. inermis is between 18-24 inches. Ideal conditions for cutting B. inermis include "hot moist weather at the time of cutting, followed by a dry period" (Sather, 1987). Managers of park areas may have even greater success if they continue mowing throughout the season.
Physical: Land managers report some success in reducing the establishment, spread and abundance of smooth brome with the use of prescribed burns (Willson & Stubbendieck, 2000). Willson and Stubbendieck (2000) recommend burning in early spring at the four or five leaf stage of smooth brome. This tactic is thought to work because smooth brome is a cool season grass that begins its growth cycle and sets seeds before native warm season grasses (i.e., C4). Therefore, a properly timed prescribed fire may reduce smooth brome abundance before it set seeds, while freeing up space and resources for native warm season grasses to flourish. According to Willson and Stubbendieck (2000), warm season grasses needed to respond and achieve a minimum of 20% coverage before the next year’s growth cycle begins for this practice to effectively reduce smooth brome populations. Rigorous field testing of this management tactic has yet to be attempted.
However, most research indicates that fire has not demonstrated an ability to effectively control B. inermis. Grilz and Romo (1994) note that tiller density, standing crop, and leaf area indices reveal that not only is B. inermis resistant to fire, but it may actually increase incidence of B. inermis as fire will restrict or kill its competitors.
Chemical: April or May applications of glyphosate at 2kg/ha has shown some ability to control spread. Paraquat is generally less effective that glyphosate (Sather, 1987).
Bromus inermis is a cool season grass. Growth phase begins in early spring and continues into the late fall. Roots develop within 5 days of germination. Seed production is variable, with plants producing between 156 and 10,080 viable seeds (Lowe & Murphy, 1955 in Sather, 1987). Seeds remain viable for 2-10 years (ANHP, 2004). Plants flower in synchrony and pollination can occur between plants up to 50m apart. B. inermis is an open pollinated plants and is self-incompatible. B. inermis can also reproduce through rhizome development which begins three weeks to six months after germination (Sather, 1987; North Dakota Department of Agriculture, Undated).
Bromus inermis is a perennial plant. Seeds remain viable for 2-10 years (ANHP, undated).
Reviewed by: Forrest P. Dillemuth, Louisiana State University
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Friday, 14 May 2010