False Brome – July 2020 Weed of the Month

false brome plants

False brome grows in clumps with flat, drooping leaf blades that stay green most of the year. Photo by Glenn Miller.

False brome is not your ordinary grass species. This introduced bunch grass spreads into shaded woodlands and can carpet the forest floor, excluding native species and increasing fire risk. Sometimes used as an ornamental grass, false brome (Brachypodium sylvaticum) first spread extensively in the Willamette Valley in Oregon and has since moved into areas of Washington and California. It has a broad native range in Europe, Asia and North Africa where it most often grows in forested areas. Unfortunately, because of this shade-tolerance, false brome poses a higher risk of invasion here in the Pacific Northwest because of our extensive forests and woodland habitats.

In King County, we first encountered false brome in a landscaped area on Vashon Island where it may have been planted or brought in accidentally. This small patch has been easily controlled because of its size and it appears not to have spread beyond the planting bed.

false brome in seed

The first false brome found in King County was in a landscape bed on Vashon Island. Photo by Linda Swartz.

false brome in seed

False brome in seed. Note the long awns and spikelets without stalks. Photo by Linda Swartz.

Sadly, the same cannot be said for the numerous patches of false brome recently discovered in east King County by our noxious weed specialists and the King County Roads vegetation management crew. There appear to be two main areas of infestation. The largest so far is in the Lake Kathleen/Lake McDonald area, where there are patches along roadsides as well as some large infestations in forested areas. The second main area is in the Mirrormount neighborhood, where initial surveys show it mostly along roadsides but also spreading into forests as well.

false brome in a woodland

False brome taking over a wooded area near Lake McDonald in east King County. Photo by Minwook Park.

According to Minwook Park, our noxious weed specialist for east King County, false brome is likely being spread through mowing as well as helped along by deer and elk, based on the patches found along wildlife trails heading into the woods. Where it has spread into forests, it is behaving like in Oregon, creating a solid carpet and excluding other plants.

false brome by a tree

False brome is adapted to forests so it poses a serious threat to King County woodland habitats. Photo by Minwook Park.

Because false brome is a Class A noxious weed and still very limited in distribution, we are focused on early detection and rapid response. The initial goal is to contain it along the roadsides and to manage the few large patches found last year, as well as new sites found this spring. Hopefully, we have found the extent of the infested areas, but more surveys may turn up new patches. Grasses are notoriously hard to identify, and it is very possible that this one has escaped our notice in other parts of the county.

false brome growing with ferns

False brome along a forest edge is difficult to spot until it has spread, but clumps of shiny green leaves can stand out once you are trained to look for it. Photo by Minwook Park.

It will take a team effort to contain this difficult invasive grass. So far all of the false brome sites are in unincorporated King County, and King County Roads has been working hard to control it on the public roadsides. When false brome is spotted on private property, Minwook and our other staff contact the property owners and offer to control it for them, or they show people how to do it themselves if that’s their preference.

false brome plants

Although false brome is a clumping grass, it spreads by prolific seeding and can create carpets of plants very quickly. Photo by Minwook Park.

It would be great to get help finding new locations, but because false brome is difficult to identify and easily confused with other grasses, it is very important to get confirmation of the species before it’s controlled. Also, we would like to know where it is growing. As with most invasive species, there is usually more around than you first suspect, so it’s important to search nearby areas for more infestations.

False brome is a perennial bunch grass that stays green most of the year. The leaf blades are lime-green, flat and arching or drooping. The flowers (called spikelets) are also drooping on tall, slender stems and either stalk-less or on short stalks. Key identification traits include hairs along the edges of the wide, flat leaves, lower stems covered with fine, even hairs, and an open leaf sheath (meaning the base of the leaf freely releases the stem when the leaf blade is pulled back). False brome looks like a true brome but differs in that the spikelets aren’t on long stalks.

false brome stems and leaf blade

False brome has soft, evenly spaced hairs on the base of the stems and leaf edges, and an open leaf sheath. Photo by Bruce Newhouse.

false brome spikelets

False brome spikelets are stalkless or on very short stalks and are drooping on the ends of slender stems. Photo by Bruce Newhouse.

There are helpful, closeup pictures of false brome on the websites listed below. However, the best way to be sure is to contact one of our noxious weed specialists or send the location and a photo through our online Report a Weed form or the King County Connect mobile app so we can check it out in person.

For more information and photos of false brome:

King County Noxious Weed Control Program

Washington State Noxious Weed Control Board

Oregon Department of Agriculture Noxious Weed Control Program

 



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4 replies

  1. Thank you for this information.

    Since Lake Kathleen is my home stomping ground and the I tend to be the neighborhood weed guy, I will aquatint myself better with this bad actor so I can be on the lookout. I’ll also post a link to this blog in our community email and Facebook groups.

    Not in my back yard! ~{:-)

    • Thank you Keith! Minwook is great at teaching people to ID this plant so feel free to reach out to him, or to encourage others to if they see any suspicious clumps!

  2. Im based just minutes from Mirrormont and run an ecology company – whats the best way for me to help at this time? Report sightings? Pull weeds? Both?
    -Scott

    • Hi Scott, what a great offer! Spotting and reporting false brome or other regulated weeds to Minwook or with our Report a Weed form would be perfect! If you feel inspired to pull tansy ragwort, I know everyone would be very grateful, but don’t worry too much about the roadsides, King County Roads is really on the ball with control so just let us know where you see it. False brome is tricky to find, so reporting it instead of controlling it might be better. Email me at sasha.shaw@kingcounty.gov and I’ll connect you with Minwook. He might have some other ideas about what would be most helpful.

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