Importance to Maryland –
Mouse barley (Hordeum murinum ssp. leporinum), also known as wall barley or hare barley, is an invasive grass that is new to the Eastern United States. The ripe seeds of mouse barley catch on to the fur of passing animals, and then, as the awns and barbs wear down over time, drop off at a distant location. However, seeds caught near the face, paws, armpits, groin, rear end, and other areas, can gradually work their way inside an animal, causing pain, and dysfunction. Dogs, cats, and horses are all documented victims of mouse barley. Presumably several species of wildlife are similarly affected. For its harm to animals, and to the people that love them, mouse barley has been chosen as this MISC Invader of the Month.
Photo caption: As summer begins, mouse barley spikes (above) turn tan. When a ripe seed breaks off from the tip of the spike, it takes the surrounding awns and a little bit of the stem with it. When the resulting dispersal unit attaches to a passing animal, or to clothes, it can be carried to distant locations. The remainder of the spike has a broken-off look that can be seen from a few feet away and, in our region, is unique to the three barley species discussed in this article. June 22, 2023. Truxton Circle, Washington, D.C.
Photo caption: Mouse barley dispersal units have an intricate system of backward-pointing barbs. Once the unit is caught up in an animal’s fur, the sharp tip can easily penetrate skin or other membranes. The common orientation of the barbs allows the unit to burrow into an animal but prevents it from being pushed outward (Brenner, 1983). The dispersal unit shown is about 1.5 inches long (3.5cm).
Physical description –
Mouse barley is a winter annual that can reach a height of 44 inches. Mowed plants tend to be shorter and somewhat prostrate. Like other members of the wheat family, it produces characteristic inflorescences called ears or spikes. Grasses can be challenging to identify, and, in our region, this one has two look-alikes. These tips will help you to tell them apart.
- Foxtail barley (H. jubatum) is also a short, introduced plant that frequents roadside habitats. You can easily recognize foxtail barley by its luxuriously long awns, lax spikes, and plain, green auricles that lack protrusions.
- Little barley (H. pusillum) is another short barley often found in disturbed habitats, however it is native. You can easily tell little barley by its narrow spikes, shorter awns, and plain, green auricles that lack protrusions.
Caption for 3-photo set: In late spring, barley plants begin to flower. The flowerheads, known as “ears” or “spikes”, can be used to tell the species apart. The spikes of foxtail, mouse, and little barley (L to R) have long, medium, and short awns, respectively. The spikes of foxtail barley (L) are somewhat lax, whereas the spikes of mouse and little barley are erect. These are photos of young, green plants. As the spikes mature, they turn tan and the awns spread out more. Credits (L to R): Matt Lavin via iNaturalist CC BY, July 22, 2009, Bozeman MT; same, May 18, 2009, Unionville NV; Eric Hough via iNaturalist CC BY NC, May 7, 2024, Rio Verde AZ.
Caption: Where the leaf blade meets the sheath, mouse barley has a white band with protrusions called auricles. Sometimes mouse barley auricles are so long that they cross over each other, as shown here. Little barley and foxtail barley lack auricles. This difference is helpful for ID even before the grasses begin to flower. June 6, 2023. Ogden Street NW, Washington, D.C.
Habitat and distribution –
Mouse barley is native to the eastern Mediterranean region, where it is found in disturbed areas, but can also show up in meadows, pastures, and farm fields. It may have arrived in California with the Spanish settlers (Cal IPC). More locally, iNaturalist records show that it was in the District of Columbia by 2017, and in Maryland by 2020, where it is found almost exclusively in hell strips and median strips. These areas may resemble the warm, wet winters and the hot dry summers of their homeland. It is too early to tell the full range of habitats that will be invaded in our region, but we do have natural meadow communities that are characterized by hot, dry soils in summer.
Caption: An entire hell strip infested with mouse barley. People and animals getting in and out of cars, or dogs being taken for a walk here, are likely to become seed dispersal vectors. Ogden St. NW, Washington, D.C. June 8, 2024.
Call to Action –
We can’t know for certain how mouse barley arrived in Washington D.C., but its appearance in hell strips hints at the possibility that someone visiting the Central or Western U.S. may have inadvertently brought it back on their shoes, socks, or even on their dog. Now that it is here, it is spreading rapidly.
We may still have a window of opportunity to eradicate this species from the Eastern U.S. At the time of this writing, iNaturalist research-grade observations suggest only small infestations in New York City and Washington, D.C. (there are no Eastern U.S. reports in EDDMapS). Please help by reporting mouse barley when you see it. This link will show you current research-grade mouse barley iNaturalist observations for Maryland and the District of Columbia.
You can also help by sharing this information with friends that own cats, dogs, or horses, and your veterinarian, and anyone you know who manages the vegetation along roads and sidewalks.
Prevention/Management –
To prevent further spread, keep pets and people out of infested areas. Small patches can be pulled. Pull plants before the seed is ripe to prevent inadvertent spread. In our area, this probably means pulling the plants after the spikes appear in April – May, because that’s when we will become alert to their presence, but before the seeds begin to ripen in late May – June. Mowing has not been shown to be an effective control method and could result in spreading the seed to new locations.
The species is effectively managed by hand pulling and glyphosate. The existing literature on chemical management focuses on pasture infestations and the findings to date don’t show a clear path forward. Research is needed on management of mouse barley in roadside settings. Whatever management approach is implemented, it must be repeated until the plants stop returning. The literature suggests that this may occur within two or three years.
If you have mouse barley on private property and need herbicide advice, please contact Extension’s Ask-An-Expert service https://ask2.extension.org/open.php. We do not encourage individuals to apply herbicides to public land, and hand pulling plants near roads could be dangerous.
Photo credits: Photos by Sara Tangren, CC-BY-NC, unless otherwise noted. Most are available for download here: https://www.inaturalist.org/observations/166412584.
References (Caution: Some publications contain photographs of wounded or dead pets.)
Angel-Caraza, J., et al. 2011. Case Report: Mouse barley awn (Hordeum murinum) migration induced cystolithiasis in 2 male dogs. Can Vet J 52:67–69 https://www.researchgate.net/publication/50990084_Mouse_barley_awn_Hordeum_murinum_migration_induced _cystolithiasis_in_2_male_dogs Cal IPC. (n.d.) Hordeum murinum. https://www.cal-ipc.org/plants/profile/horderum-murinum-profile/
Combs, M., et al. 2017. Grass seed foreign body-related disease in dogs and cats: a wide spectrum of clinical presentations. Australian Veterinary Practitioner 47(1):13-24. https://www.researchgate.net/profile/Martin-Combs/publication/316472971_Grass_seed_foreign_bodyrelated_disease_in_dogs_and_cats_A_wide_spectrum_of_clinical_presentations/links/5c985f81a6fdccd46038526b /Grass-seed-foreign-body-related-disease-in-dogs-and-cats-A-wide-spectrum-of-clinical-presentations.pdf
Mohammadi, G and K. Sardari. 2009. Ulcerative stomatitis due to Hordeum murinum: An outbreak of ulcerative stomatitis due to mouse barely (Hordeum murinum) in horse. Iranian Journal of Veterinary Science and Technology 1(1):47-52. https://ijvst.um.ac.ir/article_25242_5ab574a326c5445c16d787a1e5ce2ea6.pdf
von Bothmer, R., C. Badenf, and N. Jacobsen. Hordeum L. In: Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico [Online]. 25+ vols. New York and Oxford. Vol. 24. http://floranorthamerica.org/Hordeum. Accessed Jun 20, 2024.
Weakley, A.S., and Southeastern Flora Team. 2024. Flora of the Southeastern United States Web App. University of North Carolina Herbarium, North Carolina Botanical Garden, Chapel Hill, U.S.A. fsus.ncbg.unc.edu. Accessed Jun 20, 2024.