Indaziflam reduces downy brome (Bromus tectorum) density and cover five years after treatment in sagebrush-grasslands with no impact on perennial grass cover

Abstract

The invasive annual grass downy brome (Bromus tectorum L.) is a critical threat to the semi-arid shrublands that characterize western North America. More abundant fine fuel after invasion typically increases fire frequency in plant communities adapted to relatively infrequent burning, reducing the likelihood of native plant persistence. Currently, imazapic is most often used to manage B. tectorum, but reinvasion from the seed bank after treatment is common. Indaziflam is a newer herbicide recently labeled for use in rangelands grazed by livestock, and many research trials have demonstrated its ability to deplete invasive annual grass seed banks. We evaluated the effectiveness of indaziflam and imazapic for reducing B. tectorum density and cover over a period of approximately 5 years (57 months after treatment; MAT) at two invaded sagebrush-grassland sites near Pinedale, Wyoming. Treatments included three different indaziflam rates (51, 73, and 102 g ai ha-1) and one imazapic rate (123 g ai ha-1), and these treatments were reapplied to half of each plot 45 MAT to evaluate the effects of two sequential applications. We also measured perennial grass cover because positive perennial grass responses were observed after release from B. tectorum competition in other studies, and perennial grasses may provide resistance to B. tectorum reinvasion. Intermediate and high indaziflam rates (73 and 102 g ai ha-1 respectively) reduced B. tectorum cover and density 45 MAT, and perennial grass cover responded positively to some treatments mostly early in the study (≤ 33 MAT). Imazapic reduced B. tectorum initially, but did not affect density or cover at either site beyond 21 MAT. Reapplication did not substantially improve B. tectorum control 57 MAT in plots treated with intermediate and high indaziflam rates, suggesting that long-term control with a single indaziflam treatment may be possible in some cases.

Effects of Using Indaziflam and Activated Carbon Seed Technology in Efforts to Increase Perennials in Ventenata dubia–Invaded Rangelands

“…Our results suggest that indaziflam controls ventenata for at least 3 yr post application. Similar to our results, indaziflam effectively controlled other invasive annuals for multiple years (Sebastian et al 2016, 2017b; Courkamp et al 2022). Though ventenata control with indaziflam was substantial in the first yr post application, control improved from yr 1 to yr 2 (see Fig.…”

“…Though there appears to be a slight decrease in indaziflam activity by the third yr post application, indaziflam may substantially reduce ventenata in subsequent years. In support of this, indaziflam reduced an exotic annual grass, cheat-grass ( Bromus tectorum L.), for almost 5 yr in Wyoming (Courkamp et al 2022). Clearly, indaziflam controls ventenata and other exotic annual grasses for multiple years, making it an effective management tool to reduce their effects in plant communities.…”

“…Control of ventenata with indaziflam is of particular interest to land managers because it has a longer soil residue time compared with other preemergent herbicides commonly used in rangelands ( Brabham et al 2014 ;Sebastian et al 2017a ). It is expected to control annual grasses for at least 2 to 3 yr, though control has been observed for almost 5 yr after application (e.g., Courkamp et al 2022 ). Though indaziflam has been investigated as a control treatment for ventenata ( Koby et al 2019 ;Hart and Mealor 2021 ), these studies evaluated effects for 1 yr post application ( Hart and Mealor 2021 ) or mixed indaziflam with other herbicides ( Koby et al 2019 ).…”

Incorporation of Indaziflam into Natural Areas Management of Cheatgrass and Other Short-Lived Invasive Species: Post-Fire Assessment in a Semi-Arid Colorado Grassland

“…We found that indaziflam had good efficacy against Bromus tectorum, Bromus japonicus, and Alyssum simplex in both burned and unburned areas during the first growing season post-fire. This indicates successful depletion of the target species' soil seed banks, as reported in other studies (Germino et al 2016b;Sebastian et al 2017;Clark et al 2019;Courkamp et al 2022a) and shows promise for breaking the invader-fire cycle that can develop when annuals degrade historically perennial-dominated vegetation types (Ravi et al 2019;Humphries et al 2021). In terms of species-specific responses to fire at our site, we did not find a post-fire increase in B. tectorum as in other systems (Davies and Nafus 2013).…”

Evaluation of herbicide programs for the control of knotroot foxtail [Setaria parviflora (Poir.) Kerguélen] in bermudagrass pasture

“…However, knotroot foxtail biomass totals for the season were greatest for the indaziflam treatment compared with totals for both the nontreated control and pendimethalin (Table 4). Other studies suggest that indaziflam does not negatively affect perennial grass growth (Clark et al 2019(Clark et al , 2020Courkamp et al 2022;Hurdle et al 2020;Sebastian et al 2016Sebastian et al , 2017. Although this may be beneficial for minimizing annual weed competition with bermudagrass forage, it could allow for the further release and spread of knotroot foxtail within bermudagrass pastures.…”