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Identifying annual invasive grasses important for management

by Wyoming Livestock Roundup

Following the drought from last year, this year’s drought seems to be a favorable year for invasive grasses. The mixture of bringing in hay from other places, along with the climate, allows invasive grasses to thrive in some parts of the state. It is important to be able to identify these different invasive grasses so producers can properly manage them. 

It is important to try to manage invasive grasses because they can reduce species diversity and forage quality. Not only do they have ecological effects, but they also have an economic impact.  

To avoid costly and long-term control efforts, an Integrated Pest Management plan s needed for early detection and rapid response to contain and eradicate invasive species before they spread further.

Some of the invasive annual grasses found in parts of the state include cheatgrass, Japanese brome, ventenata, medusahead and bulblous bluegrass. Most producers are familiar with cheatgrass, Japanese brome and bulblous blugrass. However, not many are familiar with medusahead or ventenata. 


Medusahead’s seedlings emerge in the fall and re-growth occurs early in the growing season. This early regrowth of medusahead reduces soil moisture for perennial grasses. Additionally, its silica content creates thatch, which does not allow other grass seedlings to establish. 

However, medusahead seedlings can germinate in the thatch. Medusahead silica content makes it unpalatable and it has caused serious economic impacts in Western U.S. In Wyoming, medusahead is currently found in Sheridan County. 

The most cost-effective management strategy is preventing the introduction and spread of medusahead. Therefore, it is important to contact a local Extension office, Weed and Pest Control, Natural Resources Conservation Service (NRCS), U.S. Forest Service (USFS) and/or a county conservation district office if an invasive grass is suspected.  

It is important to minimize the spread of medusahead seeds from infected areas to non-infected areas. Additionally, it is important to avoid overgrazing of perennial plants as they can help prevent meduasahead from establishing and spreading. 

Medusahead can be managed using herbicide treatment, prescribed fires and revegetation. Herbicide active ingredients such as imazapic, aminopyralid, rimsulfuron and sulfosulfuron can control medusahead. However, if little-to-no desirable vegetation remains after a herbicide treatment or a prescribed burn, revegetation should be integrated. 


Ventenata is an invasive annual grass with little value as a forage species. Ventenata is documented to rapidly spread in the Western U.S. This species is currently found in Sheridan, Johnson, Campbell, Crook and Converse counties.  

Ventenata reduces forage availability for livestock and wildlife and it reduces species biodiversity. Prevention of the invasion and spread of ventenata is vital. Ventenata, like other invasive grasses, can be hard to control. 

Preventing the spread is the best management tool. To control the invasive grass and restore the ecosystem, a producer can apply herbicides. Choosing a proper herbicide to not harm the existing perennial grasses is crucial or else it can result in higher abundance of ventenata. 

Indaziflam is an effective herbicide to manage for ventenata in perennial grass stands. Management can be achieved using herbicides such as indaziflam (Rejuvra) and imazapic (Plateau). The timing of application is important for its effectiveness. 

When trying to manage these annual grasses, it is important to properly identify them. Being able to identify them early before they get out of control allows producers to manage them easier. However, if they have already taken over, there are still ways to manage them. 

For more information, contact the nearest Extension office, Weed and Pest Control, NRCS, USFS and/or a county conservation district office.

Alex Orozco-Lopez is a University of Wyoming Agriculture and Natural Resources Extension educator. He can be reached at

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