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Extension Education: Ventenata and Medusahead Update

by Wyoming Livestock Roundup

By Jaycie Arndt, UW Extension Educator

Invasive annual grasses have been and continue to be an important topic for Wyoming producers. 

Ventenata dubia (ventenata) and Taeniatherum caput-medusae (medusahead) pose a considerable threat to the state of Wyoming. Both species have negative impacts on forage quality and quantity, wildlife habitat, biodiversity and fire cycles. 


Ventenata is a small-stature, winter-annual grass. It emerges in the fall, overwinters and resumes growth early in the spring. It has dark purple nodes which are easily identifiable at all growth stages. 

As a seedling, the inflorescence is close to the stem, and as it matures, it opens into a panicle which resembles a boat mast. The seeds have bent awns which twist on the bottom half. 

Medusahead has a similar life cycle to ventenata, although it grows slightly earlier in the spring. 

In the spring, medusahead will be a bright, almost lime-green color, and then turns to a dull brown by mid-summer. It has bracts which hold seeds in place and appears as if it has two different length awns. 

These bracts will remain as seeds mature and fall from the plant, which makes it identifiable even late into the fall.  


Ventenata populations have been identified in Sheridan, Campbell, Crook, Johnson, Converse and Northern Albany counties as of the fall of 2023. 

Medusahead populations have been identified in Sheridan and Converse counties. All known Converse County populations have been treated as of 2023. 

Containment zone

The Northeast Wyoming Invasive Grasses Working Group (NEWIGWG) has established an early detection, rapid response (EDRR) framework which includes containment zones for both species. 

The ventenata containment zone begins at the Wyoming and Montana state line, follows the eastern face of the Big Horn Mountains, cuts east at Lake DeSmet, follows U.S. Highway 14/16 from Ucross to Gillette, follows Interstate 90 to the Crook and Campbell county line, and then north on the county line back to the Wyoming and Montana state line. 

Populations of ventenata found outside of the containment zone receive priority attention, while inner populations are treated as funding is available. 

The medusahead containment zone encompasses Ranchester, Dayton, Big Horn and Sheridan. NEWIGWG prioritizes treatment of medusahead outside of the containment zone, but also works towards eradication within the zone. 


Individuals who believe they have ventenata or medusahead are encouraged to bring a photo or sample to their local Weed and Pest District or University of Wyoming Extension Office. Be careful not to spread seeds by using a plastic bag for samples. 

Individuals can also report sightings through the EDDMapS app, which can be downloaded from the Apple or Google app stores. 

Jaycie Arndt is a University of Wyoming assistant research scientist in Sheridan and the NEWIGWG Coordinator. She can be reached at

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