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Invasive perennial grass spreads through the West

by Wyoming Livestock Roundup

Bulbous bluegrass, otherwise known as Poa bulbosa, is a short-lived perennial grass invasive to North America. In recent years, bulbous bluegrass has begun to spread and dominate vegetation communities in Wyoming and throughout the West. 

Bulbous bluegrass was unintentionally introduced to North America in the early 1900s. It appeared as a seed contaminant in shipments. However, in 1906, it was also introduced intentionally to be evaluated as a turf grass to be grown during winter months. It performed poorly as it matured too early and turned brown. 

Currently, bulbous bluegrass invades roadsides, rangelands, hay and crop fields. It is becoming more and more widespread in Western states as it has adapted to areas with dry summers, mild winters and winter-dominated precipitation.

Bulbous bluegrass behaves similarly to an invasive winter annual grass, as it begins growth when late fall precipitation provides adequate moisture. The grass overwinters beneath snowpack and resumes growth early in the spring. 

As spring progresses, bulbous bluegrass grows rapidly and usually produces bulblets, then turns brown in dormancy by late June. 


The major identifying characteristic of bulbous bluegrass is it produces bulblets rather than seeds.

Very few grasses in North America reproduce via bulblets. These bulblets are essentially live plants which fall from the parent plant and immediately start growing given adequate conditions. This makes plants easy to identify, as both the inflorescence and the base of plants will be bulblets. 

Other identifying characteristics of bulbous bluegrass include a ‘boat tip’ leaf blade, which looks like the front of a boat and is common in bluegrass species. 

It has mostly basal leaves with membranous ligules. It ranges in height from eight to 24 inches and is usually shallow rooted. The bulbs are usually dark purple at the base. As the plant senesces, it turns a dark purple/brown color. 


It is important to prevent the spread of bulbous bluegrass. Managing this species can become very expensive, so preventing populations from invading rangelands is the most economically efficient strategy. 

Bulblets can be moved by livestock, wildlife, infested hay, vehicles, equipment and small mammals. Be sure to keep an eye out for bulblet dispersal and for new populations so they can be treated early on. 


In small populations, bulbous bluegrass can be successfully managed via intensive hand pulling.

Mowing, however, is not a viable option for bulbous bluegrass control as it can increase infestations due to seed spread. Spring tillage may also help manage bulbous bluegrass populations, but fall tillage is less effective. 

Livestock and wildlife use bulbous bluegrass as forage in the late fall and early spring. Intensive spring grazing may reduce bulbous bluegrass infestations. Once the plant begins to mature and senesce, it becomes unpalatable to most classes of livestock. 

This means producers must be careful when grazing bulbous bluegrass, because livestock may over-utilize desirable perennial grasses when trying to avoid unpalatable bulbous plants. 

Several herbicides are effective for bulbous bluegrass control. Recent research conducted at the Sheridan Research and Extension Center found a combination of Rejuvra and Plateau at five ounces per acre, each sprayed in late fall or early spring, provide greater initial control and long-term control of bulbous bluegrass. 

With the combination of herbicides, Plateau controls existing plants and Rejuvra prevents bulblet survival in subsequent years. Plateau alone appears to provide good control of bulbous bluegrass in the first year after treatment, but the control diminishes by four years after treatment. 

Matrix also provides good control, but does cause some perennial grass damage in the first year. 

Other herbicides may be effective at controlling bulbous bluegrass under special circumstances. 

Jaycie Arndt is a University of Wyoming invasive grasses Extension educator. She can be reached at

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