Cheatgrass (Bromus tectorum L.) is one of the most significant invasive weeds of North America. Because eradication may not be a feasible goal, it may be desirable to manage cheatgrass in low-density stands below the ‘impact' stage of invasion. Little work has investigated managing such stands by single or sequential herbicide applications. We inset randomized complete block experiments with five herbicide treatments an  controls into seven different sites. Five sites were treated previously with imazapic in different years (2006-2010). Two sites – one dominated by Hesperostipa comata (Trin.&Rupr.) and one co-dominated by Pascopyrum smithii (Rydb.) and Bouteloua gracilis (Willd.exKunth) – were received treatment only in 2011 and included a simulated grazing treatment combined with herbicide.  Herbicide treatments included imazapic (70 and 105 g ai/ha), propoxycarbazone sodium (59 g ai/ha), rimsulfuron (158 g ai/ha), and a combination of tebuthiuron (170 g ai/ha) and aminopyralid (92 g ai/ha) applied prior to cheatgrass emergence in fall of 2011. We evaluated the vegetation response – including cover, biomass production, and seedbank – in summer 2012 and 2013. All herbicide treatments reduced cheatgrass cover (p = 0.0284) and biomass production (p = 0.0005) at the H. comata site in 2012 but had little effect on vegetation cover at the other sites in either year (p>0.05). Although treated repeatedly with herbicide, most desirable native species were not adversely affected. In 2013, herbicides reduced Poa secunda biomass production at the B. gracilis and canopy cover at the 5 year retreatment interval site (p < 0.05). The germinable seedbank was largely unaffected by herbicide treatments. The defoliation treatment had minimal to no effect on the plant community above- or belowground (p > 0.05). Results indicate retreatment with herbicides had limited impact on native perennial grasses, and that seedbank characteristics may not be strong indicators of aboveground vegetation response to cheatgrass control.
Oral presentation and poster titles, abstracts, and authors from the Society for Range Management (SRM) Annual Meetings and Tradeshows, from 2013 forward.