Bulbous Bluegrass
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Featured Weed: Bulbous Bluegrass Bulbous bluegrass is a perennial that has the capacity to regenerate from its root system each year. by Jane Mangold MSU LAVIN, PHOTOS BY MATT Extension Invasive Plant Specialist, Montana State University FIGURE 1. Bulbous bluegrass plants. Bulbous bluegrass (Poa bulbosa) was very prevalent from late dormancy; in essence, each bulblet is a mini-plant that can form spring through early summer in 2014 around Montana. This article roots and grow once it falls to the soil surface. The viability provides a brief overview of the species, including management of bulblets is believed to be relatively short (2 years). Bulblets recommendations, so that if 2015 proves to be another good year can be moved via livestock, wildlife, infested hay, vehicles, for bulbous bluegrass, you can be better prepared. and caching by small mammals. Interestingly, while bulbous bluegrass mainly reproduces by bulblets in its introduced range, Bulbous bluegrass identification, biology and in its native range it primarily reproduces sexually by seed. The impacts name bulbous bluegrass can also be attributed to the stems Bulbous bluegrass is a relatively small, shallow-rooted, cool- which are thickened and bulblike at the base (Figure 3). season perennial bunchgrass native to Eurasia and northern Bulbous bluegrass was accidentally introduced to North Africa (Figure 1). Because it grows new roots each season and America as a contaminant in alfalfa and clover seed. It was has a relatively short life span, it is sometimes described as an discovered in Oregon in the early 1900s. Because of its vigorous annual with “perennial tendencies.” However, it is a perennial growth and tendency to form a solid mat, its use as a pasture that has the capacity to regenerate from its root system each and turf grass was repeatedly researched in the first half of the year. This is in contrast to some other invasive grasses that you 20th century. The growth characteristics that sparked interest may be familiar with like cheatgrass (Bromus tectorum) and in bulbous bluegrass as a turfgrass are the same characteristics Japanese brome (B. japonicus). These species are annuals and that make it weedy! Bulbous bluegrass tolerates a wide range must regrow from seed each year. MSU (L) AND JANE MANGOLD (R), LAVIN PHOTOS BY MATT of environmental conditions, but is best adapted to disturbed, The leaves of bulbous bluegrass are mostly located at the base shallow soils that are moist during winter and early spring. It of the plant and have a membranous ligule (thin membrane on typically does not grow very well in soils that are continually the inside of the leaf blade at the junction of the leaf sheath moist. It has been reported in nearly every state in the U.S., but and leaf blade). The lower stems are flattened, while the upper is most common in the West. It is not listed as a noxious weed stems are wiry and round in cross-section. Bulbous bluegrass in Montana or any neighboring states. ranges in height from eight to 24 inches. Bulbous bluegrass produces very little biomass for grazing, and The panicle (inflorescence, or flowering and seed producing its palatability is confined to early to mid-spring before the grass portion of the plant) is usually dense and has a plume-like dries out. The bulblets, however, contain high levels of starch and appearance. The name bulbous bluegrasss arises from bulblets fat that are sought after by a variety of birds and small mammals. with purple bases that form on the panicle (Figure 2). Bulblets Bulbous bluegrass competes with more desirable vegetation on provide the primary means of reproduction (asexual). These rangelands. It can also invade cropland and hayfields. structures can germinate immediately without a period of 8 | big sky small acres Bulbous bluegrass management Many landowners wish to conserve and promote grass growth. Using herbicides that will selectively reduce bulbous bluegrass Bulbous bluegrass is typically not competitive in dense stands while not damaging desired grasses requires selecting the right of perennial crops like alfalfa or pasture. Therefore, maintaining herbicide and applying it at the correct time of the growing desirable competitive vegetation can be very effective for season. When using any herbicide, be sure to consult the label preventing invasion by bulbous bluegrass or for reducing for more detailed information and always follow label directions. existing infestations. Disturbance promotes bulbous bluegrass, so avoid overgrazing and other disturbances that reduce vigor of Several herbicides are labeled for bulbous bluegrass control on desirable vegetation or create bare soil. rangeland and in pastures. They include herbicides that contain the active ingredient glyphosate (e.g., Roundup®), rimsulfuron Hand pulling and digging can be used to manage bulbous (e.g., Matrix®), sulfometuron methyl (e.g., Landmark XP®), or PHOTOS BY MATT LAVIN, MSU LAVIN, PHOTOS BY MATT bluegrass because the plant is shallowly rooted; however, sulfosulfuron (e.g., Outrider®). Because glyphosate is non- FIGURE 1. Bulbous bluegrass plants. it is difficult to remove all of the basal bulbs. Mowing is not selective (will kill or stress any actively growing vegetation), it considered to be effective and may even proliferate the problem should be applied early spring prior to active growth of desired by scattering bulblets. Spring tillage can reduce bulbous perennial grasses. The other active ingredients listed above bluegrass and may be appropriate in some situations, especially are more selective than glyphosate and can be applied post- if used in conjunction with re-seeding during pasture renovation. emergent from fall to early spring. The following link provides Fall tillage is less effective. a list of herbicides that may be effective based on reports Intensive early season grazing for several growing seasons can by researchers and land managers: http://wric.ucdavis.edu/ reduce bulbous bluegrass infestations. If grazing is going to be information/natural%20areas/wr_P/Poa_bulbosa.pdf. When used, it must be applied early in the growing season because infestations are very dense and little desired vegetation remains, bulbous bluegrass generally grows earlier and faster than other be sure to integrate re-seeding with herbicide applications. perennial grasses. Do you need help identifying grasses? Check out the “Montana The effects of prescribed fire on bulbous bluegrass are not Grasses” app at www.highcountryapps.com ($4.99). The well known, but individual plants can be top-killed by fire. The app includes 105 grass and grass-like species common to survival of bulblets will depend on their location at the time of cropland, pasture, and rangeland in Montana. For help with the fire (i.e., on the plant, at the soil surface, or buried) and fire grass identification terminology, check out the MSU Extension intensity. Bulblets are most likely to be killed by fire if they are MontGuide Grass Identification Basics at http://msuextension. on the plant. As they fall to the soil surface or become buried, org/publications/AgandNaturalResources/MT201402AG.pdf. they are more likely to survive prescribed fire. PHOTOS BY MATT LAVIN (L) AND JANE MANGOLD (R), MSU (L) AND JANE MANGOLD (R), LAVIN PHOTOS BY MATT FIGURE 2. Left, panicle with purple-based bulblets. FIGURE 3. Above, stems with thickened, bulb-like bases. Spring Summer 2015 | 9.