Management of Tall Oatgrass Arrhenatherum elatius in Willamette Valley Prairies: Preliminary Report. A component of the Project Restoration and Vegetation Management of Fender’s Blue Butterfly Habitats.

Native prairies, which once dominated the landscape of the Willamette Valley, are considered among the rarest of Oregon’s ecosystems. Even though only remnants remain today, they harbor rare and endangered species such as the Fender’s blue butterfly (Icaricia icariodesfenderi) and its preferred host plant, Kincaid’s lupine (Lupinus sulphureus ssp. Kincaidii).

Invasion of weedy non-native species in the remnant prairies is of great concern to agencies and managers responsible for conserving these native ecosystems. This report focuses on control of Arrhenatherum elatius (tall oatgrass), one of the more important noxious weeds threatening Fender’s blue butterfly habitat. The first section covers the basic biology of tall oatgrass and then reviews potential control methods. The final section summarizes preliminary recommendations for controlling tall oatgrass in Willamette Valley prairies. Evidence to date suggests that mowing is the optimal choice for both controlling existing stands of tall oatgrass and preventing spread by seed dispersal.