“Medusahead will take over the West if we don't do something,” says Roger Sheley, a USDA-ARS ecologist at the Eastern Oregon Ag Research Center in Burns, OR.
First discovered in the U.S. in 1884, this annual grass, native to Eurasia's Mediterranean region, has spread through 17 Western states, infesting more than 49 million acres of rangeland, says Sheley. He and rangeland technician Lauren Svejcar manage a regional program dealing with the invasive grass.
They say medusahead invades areas where the native vegetation has been weakened by overgrazing, intense fires or cultivation. It likes dry summers and clay soils and favors former sagebrush-grass or bunchgrass areas, where it crowds out other annuals and out-competes perennial grass seedlings.
The alien invader degrades grazing and wildlife habitat and increases the risk of fire. Extreme infestations can lead to desertification.
“Livestock forage production is decreased by as much as 80% with invasion of medusahead,” Sheley says.
Livestock will graze it for a short period in spring, but the high silica content quickly makes it unpalatable. The silica also makes medusahead litter slow to decompose, forming a mat that inhibits the seedlings of more desirable species and fueling intense range fires.
Soil erodes more easily from the shallow root systems of medusahead monocultures. The loss of topsoil nutrients further discourages other plant species, until arable land eventually turns to desert.
Sheley and Svejcar recommend long-range planning to minimize losses and restore desirable plants in affected areas.
“Prevention is where the biggest bang for the buck is,” Sheley says. “For each dollar we spend in prevention we probably save $18 in management.”
Once the weed is established, though, management is the best choice. First, make a list of desired species for revegetation after the weed is controlled. Then treat existing infestations with a combination of spring plowing, slow-burning fires and herbicide applications.
Plowing and disking are best done in early spring when the weed begins to form seeds. Prescribed slow-burning fires in the spring or fall can reduce medusahead stands by 60-95%. Reducing its litter also helps in establishing desirable species.
Glyphosate (Roundup) and imazapic (Plateau) are both effective. Be-cause it does less damage to desirable species, imazapic is the best choice for most situations. Both herbicides can be applied in either spring or fall.
The final step is to prevent re-establishment by seeding a mix suitable to the site's characteristics and intended use. Sheley and Svejcar say that eliminating medusahead requires more than simply spraying weeds. Effective control requires ecological restoration and improvement, with continual monitoring as the ecosystems respond to change.
“These are complicated system management approaches,” Sheley says. “They have to be complex and long term if we are going to be successful.”
For more information, see Sheley's page under “Meet the Scientists” at oregonstate.edu/dept/eoarc/.