Annual grass invasion is transforming the western US and driving a need for restoration techniques that can both reduce abundance of exotic annual grasses and allow revegetation of native species. Pre-emergent herbicide can provide control of invasive grasses, but also tend to affect non-target natives. Indaziflam, a relatively new pre-emergent herbicide, may provide longer control of annual exotic grasses, but little is known about its effects on native seed. In this study we compare indaziflam to imazapic, a popular herbicide used in restoration efforts, to understand how indaziflam affects seeds of a native species P. spicata. We created furrows on half of our treatments to limit herbicide concentrations and potentially create a safe-site for seeding restoration species.
Results/Conclusions
During the two-year study, indaziflam provided consistent control of cheatgrass, whereas imazapic control decreased sharply with time. Imazapic and indaziflam decreased P. spicata seedling emergence 46 and 96%. Both herbicides reduced aboveground biomass and average plant size over 85% two years after seeding/herbicide application. Furrow treatments eliminated harmful herbicide effects of imazapic on P. spicata, but did not change the harmful effects of indaziflam. The results suggest that indaziflam provides stronger control of cheatgrass but also strongly inhibited P. spicata establishment which was not mitigated by furrows. Imazapic can be used with furrows to simultaneously control cheatgrass and allow successful restoration seeding, but has limited temporal control of cheatgrass that may require additional measures to ensure long-term control of invasion.