Invasive plant threatens rangelands, grazing

GRANTS PASS, Ore. – New research suggests that an invasive plant called Medusa head will keep taking over rangelands in the West, vastly reducing the grazing potential for livestock as well as wildlife.

The study published in the latest issue of the Journal of Arid Environments confirmed the hypothesis that one reason Medusa head is taking over is because most years it grows faster and for a longer period than native grasses and even other invasive plants, such as cheatgrass.

Seema Mangla, a research scholar at Oregon State University who was lead author on the study, said Medusa head already infests 2 million acres, mostly in the West, and is spreading at a rate of 12 percent a year. Once it invades an area, the grazing potential goes down by 80 percent.

“This species has a high growth rate and can stay for a longer period in the soil,” she said. “This is the main cause of the problem.”

The study looked at the growth of Medusa head in a sagebrush ecosystem in southeastern Oregon in 2008, a dry year, and 2009, a wet year. It found that Medusa head lagged behind the native bluebunch wheatgrass in the dry year, but was far ahead of it in the wet year. The study noted the dry year was far below normal and not repeated often. In both years, Medusa head grew faster and for a longer time than cheatgrass.

Livestock, deer and elk won’t eat it because the seeds have spines, known as awns, that hurt animals’ mouths, and the plant is high in the mineral silica.

Herbicides will kill it, but are too costly for use on rangelands, said Steve Van Vleet, an agricultural extension educator for Washington State University.

Because it creates mats of dead material, it also promotes fire, Mangla said.

She said herbicides, mowing and fire are treating only the symptoms of the problem, and not the cause. Research is looking into whether seeding infested areas with fast-growing nonnative grasses that livestock can eat will slow the spread of Medusa head. They include crested wheat grass and Sandberg’s bluegrass.

Medusa head was first gathered in 1884 in Oregon’s Umpqua Valley, Mangla said. It came from the Mediterranean region in the ballast of ships. A U.S. Department of Agriculture website map shows it is a problem in Oregon, Washington, California, Nevada, Utah, Idaho, Montana, Pennsylvania, New York and Connecticut.