Indaziflam Provides Long-Term Reduction of Annual Brome Grass (Bromus spp.) in Canada's Mixedgrass Prairie

Abstract

Annual bromegrasses are some of the most widespread and problematic weeds in North America and present a challenge in managing rangeland, with control options needed. The herbicide indaziflam has shown promise in long-term annual brome reduction on western United States rangeland, though how this strategy applies to northern temperate grasslands, including those of western Canada, remains uncertain. We studied the effect of indaziflam rate (0, 37.5, 75, and 150 g ai ha⁻¹) and timing (fall vs. spring) of application on long-term biomass and density of annual brome at two field sites in Canada's northern Mixedgrass Prairie. Reductions in brome were not evident until the second growing season following treatment. During the third growing season, the current recommended rate (75 g ai ha⁻¹) of indaziflam reduced brome biomass and density by at least 90% at both sites. By the fourth season, indaziflam continued to reduce brome biomass by 11% and 66%, and brome density by 76% and 95%, at the two sites, respectively. While reductions in brome biomass and density occurred at rates as low as 37.5 g ai ha⁻¹, this rate was not as reliable as higher rates of 75 and 150 g ai ha⁻¹. The timing of indaziflam application had little impact on long-term brome reduction. We conclude that a single application of indaziflam can reduce annual brome, including corn brome (Bromus squarrosus L.), in northern Mixedgrass Prairie grasslands for up to 4 years, and therefore provides another tool to manage the spread of these species.