Indaziflam controls nonnative Alyssum spp. but negatively affects native forbs in sagebrush steppe

Abstract

Non-native plant invasions can have devastating effects on native plant communities; conversely management efforts can have non-target and deleterious impacts on desirable plants. In the arid sagebrush steppe rangelands of the western United States, non-native winter annual species affect forage production and biodiversity. One method proposed to control these species is to suppress the soil seed bank using the pre-emergent herbicide indaziflam. Our goal was to evaluate the efficacy of indaziflam to control non-native annual mustards (Alyssum spp.) and to understand potential non-target effects of management on the diverse mountain sagebrush steppe plant communities within Yellowstone National Park. Six sites were established along an elevation gradient (1615 – 2437m), each with high and low Alyssum spp. infestations. We applied 63g ai ha−1 of indaziflam in late summer of 2018 and evaluated plant community cover in situ for two years after treatment, and emergence of forb species from the soil seed bank ex situ. Indaziflam was highly effective at controlling Alyssum spp. emergence for two years. Richness and Shannon’s diversity of the non-target plant community were significantly lower in sprayed plots than the control, and both decreased along the elevation gradient. These reductions were due to a decrease in perennial forbs and native annual forbs in the sprayed plots; perennial graminoids were not affected. Overall, the above ground and seed bank community composition was negatively impacted by indaziflam, and these effects were strongest for the native annual forbs that rely on annual regeneration from the seed bank. The effects of this herbicide to the non-target community should be evaluated beyond the length of our study time, however we conclude indaziflam should likely be reserved for use in areas that are severely invaded and have seed banks that are comprised of non-desirable species rather than diverse, native mountain sagebrush communities.

Soil Seed Bank Composition and Spatial Distribution in a Cheatgrass (Bromus tectorum L.)–Dominated Rangeland in Colorado, USA

“…If the seed bank were dominated by nonnative annual species that were homogenously distributed across a landscape, a treatment to deplete the entire seed bank and then reseed may make sense (Sebastian et al 2017a). However, these data suggest that a seed bank depletion treatment could deplete both the nonnative seed bank and potentially deplete a robust native seed bank at a site such as this (Meyer-Morey et al 2021).…”

“…However, the spatial and vertical distributions of the native and nonnative soil seed bank present a challenge to management of the nonnative seed bank at this site (Knapp 1996, Humphrey and Schupp 2001, Gioria and Pyšek 2016, Rayburn et al 2016). Meyer-Morey et al (2021) found that pre-emergent herbicides such as Rejuvra ® have the potential to negatively impact and deplete the seed bank of native grasses and forbs, which were large components of the seed bank here (32.5% perennial grasses, 19.5% annual forbs, and 5% perennial forbs and subshrubs). Studies have found that pre-emergent herbicides do not have a significant impact on the standing perennial vegetation of a site (Clark et al 2019), but native perennials were found relatively infrequently across the Two Road Fire site (Table 1).…”

“…This is especially true as new geographic strategies such as “Defend the Core” (see NRCS 2021 and Maestas et al 2022) gain traction and new tools become available for long-term nonnative annual control, e.g., the pre-emergent herbicide Rejuvra ® (Bayer; active ingredient: indaziflam) (Sebastian et al 2016, 2017b, Clark et al 2019). However, it is important to understand what native species seeds might also be present in the seed bank so that such management actions do not have adverse impacts on plant community assembly (Sebastian et al 2017a, Meyer-Morey et al 2021). Such pre-emergent herbicides are moderately mobile in soil, but the herbicide has been found to have its highest efficacy in the upper 2 cm of the soil (Alonso et al 2015, Sebastian et al 2017b).…”

Short-term Effects of Indaziflam on Non-native Brome Grass (Bromus spp.), Biological Soil Crusts, and the Endangered Dwarf Bear Poppy (Arctomecon humilis)

“…There is an indication that it may harm some native forbs (Meyer-Morey et al 2021), and it could possibly inhibit seed germination and the establishment of commonly used grasses for restoration practices (Terry 2021). However, White Dome Nature Preserve is not an actively seeded conservancy and the focus of this study was understanding how indaziflam would affect the key plants commonly found in ideal poppy habitat.…”

Future Direction of Fuels Management in Sagebrush Rangelands

“…Recent research (with early trials) suggests that the chemical indaziflam can control cheatgrass for ≥ 3 yr with no negative effects on perennial species richness or abundance (Sebastian et al 2017b; Clark et al 2019). However, other researchers found indaziflam can have negative impacts on native forbs, especially annuals (Meyer-Morey et al 2021). Chemicals such as tebuthiuron have been used to thin or remove sagebrush or encroaching trees to induce a response in herbaceous vegetation, but from a fuels standpoint the treatment has little impact on predicted fire behavior since sagebrush wood is left on site with no reduction in fuel bed height (Ellsworth et al 2022).…”