Weed Seed: Bromus tectorum (Downy brome)

Family

Poaceae

Common Name

Downy brome

Regulation

Secondary Noxious, Class 3 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: Occurs in AB, BC, MB, NB, NS, NT, ON, QC, SK, YT (Brouillet et al. 2016Footnote 1).

Worldwide: Native to northern Africa and temperate Eurasia with a broad distribution extending from Portugal in the west to China in the east (USDA-ARS 2016Footnote 2). Introduced in Greenland, Iceland, Japan, Australia, New Zealand, South Africa, and North and South America (Upadhyaya et al. 1986Footnote 3, USDA-ARS 2016Footnote 2). Widely distributed throughout North America and sometimes used as forage for livestock in spring and fall (Whitson et al. 1992Footnote 4, Barkworth et al. 2007Footnote 5, Beck 2009Footnote 6).

Duration of life cycle

Annual or winter annual

Seed or fruit type

Floret

Identification features

Size

  • Floret length: 9.0 - 12.0 mm
  • Floret width: 1.0 - 2.0 mm
  • Awn length: 10.0 - 18.0 mm

Shape

  • Elongate oval-shaped floret with a flared top

Surface Texture

  • Lemma and palea are papery with hyaline margins, glabrous or hairy

Colour

  • Florets are straw-yellow, may have a purplish wash

Other Features

  • Palea teeth longer than 1.0 mm.
  • Floret is curved away from the palea.
  • Caryopsis is usually dark purple, can be reddish-brown.

Habitat and Crop Association

Dry areas, sand dunes, cultivated fields, pastures, rangelands, along railway lines and roadsides, and in disturbed areas (Darbyshire 2003Footnote 7, Barkworth et al. 2007Footnote 5). A weed of winter cereals, alfalfa and grass fields, orchards and vineyards, pastures and grasslands (Morrow and Stahlman 1984Footnote 8, Upadhyaya et al. 1986Footnote 3, CABI 2016Footnote 9).

In western North America it dominates large areas of sagebrush and mixed grass prairie ecosystems (Ogle et al. 2003Footnote 10, Barkworth et al. 2007Footnote 5, Beck 2009Footnote 6). Commonly occurs on dry, mostly alkaline, sandy to loamy soils (Peeper 1984Footnote 11).

General Information

Downy brome was accidently introduced to western North America with cereal crops in the late 1800s, and was deliberately seeded in some pastures for forage and spread rapidly from there (Mack 1981Footnote 12). It is now considered the most widespread and damaging invasive annual grass in western and midwestern grasslands (Finnerty and Klingman 1962Footnote 13, Rinella et al. 2013Footnote 14).

It has a dual role as a serious weed and important forage, and is still used for early spring forage in the intermountain and Pacific Northwest regions (Upadhyaya et al. 1986Footnote 3, Barkworth et al. 2007Footnote 5). It is a prolific seed producer and common seed contaminant (Whitson et al. 1992Footnote 4).

Similar species

Barren brome (Bromus sterilis)

  • Barren brome has a similar elongate shape with an awn of similar length, and is also curved away from the palea.
  • Barren brome has small palea teeth, a brown caryopsis that can be flat or folded and the lemma is 14.0 - 20.0 mm long. Downy brome has long palea teeth, a purple, flat caryopsis and the lemma is 9.0 - 12.0 mm long, shorter than barren brome.

Photos

Figure 1 - Downy brome (Bromus tectorum) florets and spikelets
Downy brome (Bromus tectorum) florets and spikelets
Figure 2 - Downy brome (Bromus tectorum) floret
Downy brome (Bromus tectorum) floret
Figure 3 - Downy brome (Bromus tectorum) floret, palea teeth
Downy brome (Bromus tectorum) floret, palea teeth
Figure 4 - Downy brome (Bromus tectorum) florets
Downy brome (Bromus tectorum) florets

Similar species

Figure 5 - Similar species: Barren brome (Bromus sterilis) florets
Similar species: Barren brome (Bromus sterilis) florets
Figure 6 - Similar species: Barren brome (Bromus sterilis) palea teeth
Similar species: Barren brome (Bromus sterilis) palea teeth
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