Medusahead and Ventenata in the Northern Great Plains Ecoregion: Invasion History and Management Efforts

By Brian Mealor, Beth Fowers and Luke Sander. Presented at the Western Society of Weed Science annual meeting (2018)


The invasive winter annual grasses medusahead (Taeniatherum caput-medusae) and ventenata (Ventenata dubia) have a relatively long history of spread and impact in the Intermountain West. In 2016, self-sustaining populations of both species were documented in Sheridan County, Wyoming, representing the first known populations of each species in the Great Plains region.

The Northeast Wyoming Invasive Grasses Working Group formed in direct response to these new invasive grass populations with a primary goal of minimizing impacts to rangelands for wildlife and agriculture by reducing, containing, or eradicating medusahead and ventenata in northeast Wyoming. The working group is implementing an EDRR approach by collecting and sharing distribution data, strategically implementing control actions, and monitoring efficacy of treatments.

In 2017, more than 22,000 acres were intensively surveyed for presence of medusahead and ventenata, with significantly more acreage informally added to the species distribution via collaborators and citizen-scientists. While the current known distribution of medusahead is relatively restricted, the outer boundaries of the known ventenata range in Wyoming went from one observation prior to 2016 to well over 1 million acres of gross acres in February 2018.

Observations from the collaborative working group emphasize the importance of education and outreach in EDRR programs to the contributions of diverse partnerships in such an effort. Future efforts will incorporate vector-pathway analysis coupled with remote sensing to prioritize high-likelihood sites of future invasion for medusahead.

Click here to see a poster describing survey methods, distribution, and management of invasive grasses in the project area.

The following expanded information was provided by Dr. Brian Mealor, Director and Associate Professor, Sheridan Research and Extension Center, Sheridan, Wyoming.

  • Herbicide treatments developed by the working group focused primarily on medusahead locations as part of an eradication goal. As more distribution data is gathered, the focus of the program may shift from eradication to containment and control.

  • All treated areas had both medusahead and ventenata; however, medusahead has been the primary target.

  • The combination of Milestone® specialty herbicide at 7 fluid ounces per acres (fl oz/A) in combination Plateau at 7 fl oz/A was selected for application based on:

  1. Grazing flexibility

  2. Inconsistent control results with Plateau alone across annual grasses, although field research conducted in the West shows good efficacy on medusahead.

  3. Field trials conducted in California with Milestone indicate medusahead suppression.

  4. Significant infestations of sulfur cinquefoil (Potentilla recta) occur in combination with medusahead and ventenata. Milestone provides excellent control of sulfur cinquefoil.

  • Aerial application volume was 5 gallons per acre applied prior to annual grass emergence or early post emergence.

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Milestone specialty herbicide is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.

When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. Consult the label before purchase or use for full details. Always read and follow label directions.