Effect of perennial grasses on Canada thistle (Cirsium arvense) control

An experiment was conducted near Scottsbluff, NE, to assess three technique s for establishing perennial grasses in pasture sites and to evaluate the e ffectiveness of five perennial grasses compared with herbicide or mowing fo r Canada thistle control. Perennial grass density 9 mo after seeding and pe rennial grass biomass 12 mo after seeding both followed the same trend, ind icating that preplant rototilling improved perennial grass establishment. A fter 3 yr, Canada thistle control was greater than 90% in plots where peren nial grasses had been established utilizing preplant rototilling, and compe titive grasses were as effective as yearly applications of clopyralid at 0. 55 kg/ha for controlling Canada thistle. Averaged across two studies conduc ted for 3 yr, hybrid wheatgrass, intermediate wheatgrass, Russian wildrye, tall fescue, and western wheatgrass provided 85, 74, 76, 78, and 66% Canada thistle control, respectively.