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Invasive exotic annual grasses are replacing native plants in the vast sagebrush steppe rangelands of western North America. Efforts to control exotic grasses and restore perennials have had mixed success.

More information is needed on the most effective strategies for how, when, and where to target treatments. Researchers from Boise State University and USGS studied how the timing and type of restoration strategy, including herbicide spraying and seeding or planting native perennials, influenced restoration outcomes in a severely invaded area in southern Idaho. The results of the experiment showed that exotic annual grasses were strongly reduced for up to three years by the new herbicide indaziflam, trade name RejuvraTM, and the effects were greater with more post-spray precipitation. The current standard herbicide, imazapic, was less effective. The study also found that several years of seeding and planting resulted in no establishment of native perennials. This study shows that indaziflam is an effective tool for reducing exotic annual grasses in challenging restoration conditions, particularly when application is timed with suitable rainfall. 

Donaldson, R., and Germino, M.J., 2022, Intra-site sources of restoration variability in severely invaded rangeland- strong temporal effects of herbicide-weather interactions; weak spatial effects of plant-community patch type and litter: Ecological Solutions and Evidence, v. 3, no. 3, e12172.

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