Plant community biodiversity, biocrusts, and perennial vegetation increase and fire risk decreases with indaziflam control of invasive annual grasses

Authors: Davies, Kirk; O'Connor, Rory; Copeland, Stella; Bates, Jonathan

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Annual grass invasion in the western U.S. decreases biodiversity, biocrusts, and perennial vegetation. Indaziflam, a more recently developed pre-emergent herbicide with longer soil activity, is increasingly used for annual grass control, yet reports of its effects on plant biodiversity, biocrusts, and perennial vegetation are inconclusive. We investigated the effects of indaziflam application at 14 annual grass-invaded sites. Perennial vegetation cover and density, plant biodiversity, and biocrusts increased substantially with indaziflam control of annual grasses. Indaziflam appears to be effective at controlling invasive annual grasses for multiple years and promoting perennial vegetation, biocrusts, and plant biodiversity. These results are of interest to other scientists, land managers, restoration practitioners, and livestock producers.

Technical Abstract: Annual grass invasion in the western U.S. 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 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 three years post-treatment. 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 to 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.