Non-target effects and soil persistence of indaziflam: implications for seed-based restoration of cheatgrass-invaded landscapes in the Colorado Front Range

Abstract

Invasive species threaten ecosystems around the world. In the grasslands and shrublands of western North America, invasive annual grasses, especially Bromus tectorum (cheatgrass or downy brome), pose ecological and economic threats through their inhibitory interactions with native species, exacerbation of wildfires through increased fine fuel loads, and poor forage and habitat quality. As a winter annual species, cheatgrass also possesses a phenological advantage that makes it especially difficult to eradicate. Indaziflam, a pre-emergent biocellulose inhibiting herbicide with residual soil activity, has established a new paradigm of control for cheatgrass and other invasive annual grasses. Indaziflam is highly effective in reducing the cover of cheatgrass for at least two to three years without harming established perennial grasses. However, the effects of indaziflam on non-target species are less clear. Given that indaziflam is used pre-emergence, it may inhibit the germination of non-target species as well, which is a concern for land managers, especially when practicing seed-based restoration. We conducted a greenhouse study to assess the dose-response relationship between indaziflam and native species commonly used for seed-based restoration in the Colorado Front Range, Colorado, USA. We also conducted a field study to assess the quantities of indaziflam residue in various soils in sites treated with indaziflam in the Colorado Front Range at varying points in the past. First, I will review the literature on indaziflam as it pertains to its mechanism of action, target impacts, and non-target impacts. Next, I will provide an overview of the greenhouse and field studies. Using the filter framework of community assembly, I argue that while B. tectorum acts as a biotic filter to native species establishment and its control is vital for restoration of invaded landscapes, indaziflam may also act as an unintentional abiotic filter to native species establishment.