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Photo: Medusahead infesting open range.
ARS scientists are developing an ecologically based strategy to control medusahead, an invasive species that has infested millions of acres in western states. Photo courtesy of Kirk Davies, ARS.

Photo: Medusahead (Taeniatherum caput-medusae

Medusahead (Taeniatherum caput-medusae), an invasive species that has decimated native plant communities, degraded wildlife habitat and reduced forage quality for grazing animals including cattle. Photo courtesy of Kirk Davies, ARS.

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Challenging Weed Meets its Match in Field Trials

By Jan Suszkiw
December 22, 2009

In Oregon, California and other western states, infestations of medusahead have marched across rangeland habitats like the Genghis Khan of grasses. But at the base of Steens Mountain in southwestern Oregon, a small but stubborn band of defenders—desert wheatgrass plantings— have held fast against the invader, offering hope of a new, ecologically based approach to controlling it.

Agricultural Research Service (ARS) rangeland scientist Kirk Davies is monitoring the Steens Mountain "standoff" as part of a broader research effort at Burns, Ore., to develop new tools and strategies for land managers to use in controlling medusahead, Taeniatherum caput-medusae. This invasive species infests millions of acres there and in other western states. It has decimated native plant communities, reduced forage quality, degraded wildlife habitat and caused other harm, according to Davies, who works at the ARS Range and Meadow Forage Management Research Unit in Burns.

He and ARS ecologist Roger Sheley and range technician Aleta Nafus first established the desert wheatgrass, Agropyron desertorum, in February 2006 as a dozen 49- by 33-foot bands on the leading edge of a medusahead infestation near the foothills of Steens Mountain. Beyond the bands lay undisturbed communities of sagebrush, squirreltail, needlegrass and other native plants.

In June 2008, the team measured the density and canopy cover of medusahead whose seed had managed to spread beyond the desert wheatgrass barriers and become established in the plant communities. Medusahead spread data also was collected from a dozen barrier-free sites.

The team's analysis, presented in Oregon State University's 2009 Field Day Report earlier this year, showed that native plant communities without the barriers harbored more medusahead than those with the barriers—a difference of more than 40-fold. Davies attributes the reduction to the ability of wheatgrass to compete for soil resources and potentially snare wind-blown medusahead seed.

Future research could focus on fine-tuning the approach and ensuring the compatibility of desert wheatgrass with native species—its "protectees." Ideally, the barriers would be integrated with other measures, including prescribed grazing and judicious use of herbicides.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.