Does applying indaziflam and imazapic together improve restoration of annual grass-invaded rangelands?

Authors: Davies, Kirk; PRATHER, TIM - University Of Idaho; JONES, LISA - University Of Idaho; Guetling, Christie

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2025
Publication Date: 6/9/2025
Citation: Davies, K.W., Prather, T.S., Jones, L.C., Guetling, C.H. 2025. Does applying indaziflam and imazapic together improve restoration of annual grass-invaded rangelands?. Rangeland Ecology and Management. 102:88-95. https://doi.org/10.1016/j.rama.2025.06.005.
DOI: https://doi.org/10.1016/j.rama.2025.06.005

Interpretive Summary: Restoration of perennial vegetation in annual grass-invaded rangelands is a high priority. Of particular interest is the effects of using both indaziflam and imazapic herbicides in tandem compared to only using indaziflam. We investigated the effects of applying indaziflam individually and in combination with imazapic at three sites. Applying indaziflam and imazapic in tandem provided better control of annual vegetation and promoted perennial vegetation. Applying indaziflam individually controlled annual vegetation, but did not generally generate a response from perennial vegetation. These results suggest that applying indaziflam and imazapic in tandem may be an effective strategy for controlling invasive annual grasses and promoting co-occurring perennial vegetation. This information is of interest to land and weed managers, wildlife biologist, ecologists, and other scientists.

Technical Abstract: Invasive annual grasses are degrading millions of hectares of Intermountain West rangelands. Restoration of perennial vegetation in annual grass-invaded rangelands is a high priority. Of particular interest is controlling annual grasses in rangelands that still have co-occurring perennial vegetation. The goal of restoration actions in these communities is to control the annual grasses and promote co-occurring perennial vegetation. Indaziflam and imazapic, applied as pre-emergent herbicides, have both been used for this purpose. Indaziflam often has less than desired control in the first year but can control annual grasses for multiple years. In contrast, imazapic has effective control in the first year, but control is short-lived. Land managers have recently started tank-mixing these two herbicides to potentially alleviate their individual shortcomings and theoretically achieve more effective, long-term annual grass control. However, little is known about the effectiveness of applying these herbicides in tandem, particularly compared to just applying indaziflam, and the effects on co-occurring perennial vegetation. We investigated the effects of applying indaziflam individually and in combination with imazapic at three sites (two in Oregon and one in Washington). Applying indaziflam and imazapic in tandem provided better control of annual vegetation and promoted perennial vegetation, though it appears site differences influenced treatment effects. Applying indaziflam individually controlled annual vegetation, but did not generally generate a response from perennial vegetation. Tank-mixing indaziflam and imazapic improved first year control compared to only applying indaziflam, but control was still better in the second year after treatment, suggesting that a greater rate of imazapic than used in this study may be needed to achieve better first year control. The results of this study suggest that applying indaziflam and imazapic in tandem may be an effective strategy for controlling invasive annual grasses and promoting co-occurring perennial vegetation.