Short-term Response of Holcus lanatus L. (Common Velvetgrass) to Chemical and Manual Control at Yosemite National Park, USA

One of the highest priority invasive species at both Yosemite and Sequoia and Kings Canyon national parks is Holcus lanatus L. (common velvetgrass), a perennial bunchgrass that invades mid-elevation montane meadows. Despite velvetgrass being a high priority species, there is little information available on control techniques. The goal of this project was to evaluate the short-term response of a single application of common chemical and manual velvetgrass control techniques. The study was conducted at three montane sites in Yosemite National Park. Glyphosate spot-spray treatments were applied at 0.5, 1.0, 1.5, and 2.0% concentrations, and compared with hand pulling to evaluate effects on cover of common velvetgrass, cover of other plant species, and community species richness. Posttreatment year 1 cover of common velvetgrass was 12.1% ± 1.6 in control plots, 6.3% ± 1.5 averaged over the four chemical treatments (all chemical treatments performed similarly), and 13.6% ± 1.7 for handpulled plots. This represents an approximately 50% reduction in common velvetgrass cover in chemically- treated plots recoded posttreatment year 1 and no statistically significant reduction in hand pulled plots compared with controls. However, there was no treatment effect in posttreatment year 2, and all herbicide application rates performed similarly. In addition, there were no significant treatment effects on nontarget species or species richness. These results suggest that for this level of infestation and habitat type, (1) one year of hand pulling is not an effective control method and (2) glyphosate provides some level of control in the short-term without impact to nontarget plant species, but the effect is temporary as a single year of glyphosate treatment is ineffective over a two-year period. Nomenclature: Glyphosate; common velvetgrass, Holcus lanatus L. Management Implications: This study was designed to evaluate short-term effects of a single application of chemical and mechanical control techniques on Holcus lanatus L. (common velvetgrass) cover and nontarget plant cover and species richness. Our results showed that various glyphosate concentrations were equally effective at reducing cover of common velvetgrass, and that there were no statistically significant effects of treatments on nontarget cover and species richness. A one-time spot spray application was effective at reducing common velvetgrass in the post-treatment year 1, but not longer. These spot-spray herbicide treatments, even at the highest concentrations, did not have detrimental effects on nontarget species. This is particularly important where land management objectives are not just to control invasive plant infestations but also to support native species, special status plants, or traditionally used plants (i.e., plants species that are important in ongoing American Indian traditional cultural practices such as those involving ceremony, subsistence and artistry). Despite the lack of herbicide impacts to nontarget species at any of the concentrations evaluated, the lowest concentration (0.5%) would be recommended because higher concentrations were no more effective at controlling velvetgrass. Despite the statistically significant reduction in common velvetgrass cover during posttreatment year 1, 6.3% common velvetgrass cover still remained, and the reduced cover effect was gone by posttreatment year 2. This study suggests that glyphosate treatments could be an option to control common velvetgrass, but one application will not maintain control after the first year. In order to gain long-term control, managers could experiment with glyphosate treatments repeated annually or even multiple times per year to control infestations. Hand pulling common velvetgrass at these densities for only one year was ineffective at controlling common velvetgrass. Moreover, studies have suggested that repeated hand pulling of velvetgrass and the associated soil disturbance could promote local increases in non-native species.