A new field study in Oregon confirms that invasive medusahead weeds can take over range land from most other grass species, representing a threat of spreading across much of the West.

That could disrupt native ecosystems and make millions of acres of grazing land worthless, report Oregon State University and U.S. Agricultural Research Service scientists.

The recent report represents one of the most extensive studies to date comparing the relative growth rate of the invasive weed with that of other species.

Researchers reveal that if medusahead is allowed to flourish, its faster growth rate and longer period of growth can produce more biomass than that of cheatgrsss, another invasive species long considered a major foe on the range.

"Medusahead is now spreading at about 12% a year over 17 western states," says Seema Mangla, an OSU College of Forestry researcher.  Once established, the weed is highly difficult to eradicate.

"It displaces native grasses, and even other invasive species that animals can still eat," adds Mangla. "Unless we do more to stop it, medusahead will take over much of the native grassland of the West."

"This is a devil species," she says.

Researchers are working to identify some other grass species, including crested watergrass and Sandberg's bluegrass, that may be able to compete with medusahead, reduce its spread and preserve the grazing value of land, Mangla notes.

However, medusahead has not been the focus of much research compared with other threats such as cheatgrass, even though it ultimately poses a far greater threat for the West, she says.

Cheatgrass is considered to be a serious problem on more than 50 million acres in the West, but grazing animals do eat this invasive weed. The new study finds that cheatgrass and native grasses may eventually be replaced by medusahead, which can eliminate 80% of the grazing value of land.