False brome (also called slender false brome)
False brome is a perennial bunch grass native to Eurasia and North Africa that generally stays green throughout the year. It has spread extensively in areas of western Oregon and has begun to spread to Washington State. It is highly invasive in shaded woodlands, open prairies, and roadsides and can out-compete native forest understory and grassland vegetation.
Legal status in King County, Washington
False brome is a Class A Noxious Weed in Washington State due to its limited distribution in the state and the potential for significant impact to state resources. Public and private landowners are required to control this plant when it occurs on their land. For more information see Noxious weed lists and laws.
Because of the difficulty in distinguishing this plant from more widespread weeds, we recommend contacting the noxious weed program for a positive identification before removing. There are very few records of this plant in King County, so if you do find false brome in King County, please report the location right away.
Identification (see below for more photos)
- Leaf blade is flat and lax (floppy), 1/4 to 1/3 inch wide, and distinctively bright green
- When held up to the sky, a fringe of fine hairs is easily seen around the edge of the leaf
- The leaf sheath (the base of the leaf that surrounds the stem or culm of the grass) is open and freely releases the stem when pulled back
- Lower stem is thickly covered with fine, even hairs
- Young plants look somewhat like a many-legged spider spread out over the ground
- Mature plants have a graceful, nodding form (both leaves and flowers)
- Mature stands form solid mats of plants 12 to 18 inches high
- Flower spikelets droop and have very short or no stalks
Habitat and impact
False brome can quickly become the dominant species in forest understories or open grasslands. In the Pacific Northwest, false brome is most abundant in oak woodlands and open grasslands in the Willamette Valley in Oregon, but is also found in other areas such as southwest Washington. It grows well in shade or sun, moist or dry soils, and can be found from low elevations up to 3500 feet. Individual bunches spread out and merge into solid mats of plants that can overwhelm other vegetation and prevent seed germination. In commercial forests, false brome creates the perfect habitat for rodents that damage tree seedlings and in oak woodlands false brome can suppress the germination of oak seedlings. False brome appears to have low palatability for wildlife and livestock. This grass also appears to be resistant to fire, resprouting within two weeks of a burn, and may increase fire risks due to the build up of a heavy layer of thatch.
Growth and reproduction
False brome blooms between June and September. Although plants do not spread by rhizomes, individual plants grow closely together and form dense, monotypic patches. False brome reproduces through seed. Seeds appear to be fairly short-lived but no research has been done on seed viability.
Prevention: Seeds of false brome can be carried on shoes and vehicles, so special care should be taken to clean off after entering areas infested with this plant. Watch for new patches of this plant especially after other grasses have started to turn brown (August to November or later).
Small patches: Isolated plants can be dug out before they are in seed.
Larger patches: Plants can be sprayed with a non-selective herbicide such as glyphosate (e.g. Roundup) from mid-summer through fall or after the rainy season begins in fall or with a grass-specific herbicide such as Poast (see label for timing). To reduce the amount of herbicide used, a multi-year mowing regime can be used to exhaust the seed bank before starting herbicide treatment. A combination of mowing in early July followed with a fall treatment of glyphosate is also effective. Please refer to herbicice labels for site specific control information and refer to the PNW Weed Management Handbook for additional information on herbicide use. To reduce costs and environmental impacts, please use an Integrated Pest Management approach to weed control.
Intensive grazing may also be effective in suppressing false brome. Other methods for controlling large infestations are being researched. See the False-brome Working Group website for more information.
Follow up is critical to successful eradication of false brome. Plan to go back and clean up the infested area each year for several seasons in order to exhaust the seed bank and find any survivors. Visit the site in early summer to get to plants before they set seed.
Additional information on false brome
False brome (Brachypodium sylvaticum) photos - click thumbnail for larger image
Photos on this page courtesy of Bruce Newhouse and Glenn Miller. Please do not use these images without permission from the photographers.