Rangeland Grass Species Tolerance to pre-plant applications of Aminopyralid and Aminocyclopyrachlor


One strategy to achieve long-term perennial weed management involves integrating chemical control with the establishment of competitive plant communities. Establishing native plant communities or plant communities that are dominated by native species is considered desirable in many situations. The problem is that information about the relative sensitivity of native species to herbicide residues and techniques that might reduce any negative impacts from these soil residues are not readily available. This study was initiated to examine the impacts of application timing, herbicide rate and herbicide combinations on native grass establishment.

Picloram, aminopyralid, clopyralid, aminopyralid plus clopyralid, aminopyralid plus metsulfuron methyl, and aminocyclopyrachlor were applied pre-plant in July and September 2009 to a prepared seedbed. In April 2010, ten cool and seven warm season native grasses were seeded perpendicular to the herbicide treatments. Grass biomass was determined in September 2010. None of the experimental factors (application timings, rates or herbicide combinations) significantly reduced native grass biomass when compared to hand-weeded controls; however, results indicated that individual species responded differently to these factors. Plant responses could not be adequately explained by functional groupings (cool versus warm season), for example, Canada wildrye (cool season), slender wheatgrass (cool season), galleta grass (warm season) and sideoats grama (warm season) were found to be the most tolerant species. These data suggest that pre-plant applications of these herbicides made either the spring or fall prior to grass seeding can be used to assist in the establishment of native grasses by controlling otherwise competitive weeds.


by Cameron Douglass, Joseph D. Vassios, Scott Nissen, Vanelle F. Peterson; In B McCloskey (Ed), Proceedings of the Western Society of Weed Science, Volume 64. Spokane, Washington, USA 7-10 March 2011.