Effects of Indaziflam Control of Annual Grasses on Biodiversity, Biocrusts, Perennial Vegetation, and Fire Probability

Annual grass invasion in the western United States decreases biodiversity, biocrusts, and perennial vegetation and escalates the risk of large frequent wildfires. These effects degrade critical wildlife habitat and reduce quality livestock forage. In addition, altered fire regimes threaten life and property as well as greatly increase fire suppression costs. Controlling annual grasses to negate these negative impacts is a common management objective. Indaziflam, a more recently developed pre-emergent herbicide with longer soil activity, is increasingly used for annual grass control. More information on the effects of indaziflam on plant biodiversity, biocrusts, and perennial vegetation is needed because of contradictions in reported effects and inconclusive results. We investigated the effects of indaziflam application at 14 annual grass-invaded sites in bunchgrass rangelands in eastern Oregon. Ventenata ( Ventenata dubia (Leers) Coss.) and medusahead ( Taeniatherum caput-medusae (L.) Nevski) were the dominant annual grasses at the study sites. Indaziflam was applied at a rate of 73 g ai · ha −1 in late August to early September in either 2019 or 2021. Plant community response to indaziflam application was measured for 3 yr posttreatment. Indaziflam effectively controlled invasive annual grasses for the duration of the study. Perennial vegetation cover and density increased substantially with indaziflam control of annual grasses. Plant biodiversity increased with indaziflam application, with it being 40% greater in the indaziflam treatment compared with the untreated control by the third year. Indaziflam control of annual grasses resulted in considerable increases in biocrusts and bare ground, and decreases in litter. The cumulative effects suggest that indaziflam increased plant community resistance to reinvasion by annual grasses and decreased wildfire probability. Indaziflam appears to be effective at controlling invasive annual grasses for multiple years and promoting perennial vegetation, biocrusts, and plant biodiversity.