Revegetating spotted knapweed infested rangeland in a single entry

Introducing and establishing competitive plants is essential for the succes sful management of spotted knapweed (Centaurea maculosa Lam.) infested rang eland where a desirable understory is absent. Our objective was to determin e a herbicide-mix that would maximize grass establishment in spotted knapwe ed-cheat-grass (Bromus tectorum L.) bluegrass (Poa pratensis L.) infested r angeland in a single fall application. On 2 sites in Montana, 8 herbicide t reatments [none, glyphosate (N-[phosphhonometyl] glycline) at 0.5 kg a.i. h a(-1), picloram (4-amino-3,5,6-trichloropicolinic acid, potassium salt) at 0.14 kg a.i. ha(-1), picloram at 0.28 kg a.i.ha(-1), clopyralid (3,6-dichlo ro-2-pyrdinecarboxylic acid, monoethanolamine salt) at 0.21 kg a.i. ha(-1) plus 2,4-D (2,4-dichlorophenoxyacetic acid) at 1.12 kg a.i. ha(-1), piclora m at 0.14 kg a.i. ha(-1) plus glyphosate at 0.5 kg a.i. ha(-1), picloram 0. 28 kg a.i.ha(-1) plus glyphosate at 0.5 kg a.i. ha(-1), and clopyralid 0.2 kg a.i. ha(-1) plus 2,4-D at 1.12 kg a.i. ha(-1) plus glyphosate 0.5 kg a.i . ha(-1)] and 3 seeded grass species ['Luna' pubescent wheatgrass [Thinopyr um intermedium (Host) Barkworth & D.R. Dewey], bluebunch wheatgrass [Pseudo rogneria spicata (Pursh.) Love], and 'Bozoyski' Russian wildrye [Psathyrost achys junceae (Fisch.) Nevski] were applied in a split-plot design with 4 r eplications in the late-fall of 1994 and 1995. Spotted knapweed and grass d ensity were measured in 1995, 1996, and 1997, and biomass was measured in 1 997 at peak standing crop. Density data were analyzed as a split-split-plot in time, and biomass data were analyzed as a split-plot using analysis of variance. By the end of the study picloram applied at either 0.14 or 0.28 k g a.i. ha(-1) in the late-fall consistently yielded lowest spotted knapweed density and biomass. Initially, glyphosate alone lowered spotted knapweed density and increased grass biomass compared to that of the control. Howeve r, glyphosate treated plots had more spotted knapweed and less seeded grass established by the end of the study. 'Luna' pubescent wheatgrass consisten tly yielded the high test density and biomass of the seeded grasses. We bel ieve a single-entry revegetation program applying picloram in late-fall com bined with a fall-dormant seeding will maximize seedling establishment in s potted knapweed infested rangeland.