Revegetating spotted knapweed infested rangeland in a single entry

Abstract

Introducing and establishing competitive plants is essential for the successful management of spotted knapweed (Centaurea maculosa Lam.) infested rangeland where a desirable understory is absent. Our objective was to determine a herbicide-mix that would maximize grass establishment in spotted knapweed-cheatgrass (Bromus tectorum L.) bluegrass (Poa pratensis L.) infested rangeland in a single fall application. On 2 sites in Montana, 8 herbicide treatments [none, glyphosate (N-[phosphonomethyl] glycine) at 0.5 kg a.i. ha(-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-dichloro-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), picloram 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 [Thinopyrum intermedium (Host) Barkworth D.R. Dewey], bluebunch wheatgrass [Pseudorogneria spicata (Pursh.) Love], and 'Bozoyski' Russian wildrye [Psathyrostachys junceae (Fisch.) Nevski] were applied in a split-plot design with 4 replications in the late-fall of 1994 and 1995. Spotted knapweed and grass density were measured in 1995, 1996, and 1997, and biomass was measured in 1997 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 kg 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. However, glyphosate treated plots had more spotted knapweed and less seeded grass established by the end of the study. 'Luna' pubescent wheatgrass consistently yielded the high test density and biomass of the seeded grasses. We believe a single-entry revegetation program applying picloram in late-fall combined with a fall-dormant seeding will maximize seedling establishment in spotted knapweed infested rangeland.