Inter- and Intraspecific Variation in Native Restoration Plants for Herbicide Tolerance

Choosing appropriate plant materials for restoration projects can affect establishment and persistence of desirable species. In situations where herbicides are used to manage invasive weeds, plant materials able to tolerate herbicides at early growth stages could increase probability of successful restoration of vegetation. However, little is documented regarding relative herbicide tolerance of native species commonly used in restoration and information regarding intraspecific variation for such characteristics is missing. We conducted a greenhouse study in 2010 and repeated in 2011 to investigate seedling response of 17 desirable species (27 germplasm), Russian thistle, and downy brome to aminocyclopyrachlor, a relatively new herbicide with potential applications in reclamation and restoration. We applied aminocyclopyrachlor at six rates between 10 and 320 g ha^–1 30 days after planting. Grasses were in the three to five leaf stage and forbs and shrubs were less than five cm tall at the time of herbicide application. We used a log-logistic model to estimate dry weight reduction in response to aminocyclopyrachlor rate. Russian thistle biomass was reduced 95% at 120 g ha^–1. At that same aminocyclopyrachlor rate, grass biomass was reduced 0 to 48% and flax and sagebrush species were reduced ≥ 77%. We document variation among and within species for relative tolerance to this herbicide. If aminocyclopyrachlor were used in a restoration project for postemergence control of Russian thistle, most grasses in this experiment would experience negligible biomass reduction whereas the selected sagebrush and flax species were highly susceptible at this early growth stage even at low aminocyclopyrachlor rates.