Effect of Aminopyralid on Desirable Forb Species

Native forbs are important for plant community function and diversity, and provide food and cover for wildlife. Field studies have been conducted throughout the western United States to determine the impact of herbicides applied to control invasive weeds on native forbs. However, locating adequate populations of native forbs for evaluation of tolerance to herbicides is often difficult: The susceptibility of nine native prairie forbs to aminopyralid applied at 30 to 120 g ha(-1) was evaluated in a greenhouse study and results compared to the same or similar species in field trials. Forb susceptibility to aminopyralid varied by species. Of the forbs evaluated, azure aster, purple coneflower, and closed bottle gentian were the most tolerant to aminopyralid while prairie coneflower, great blue lobelia, harebell, and white prairie clover were the most susceptible and likely would be killed in the field. Blanket flower and showy goldenrod were moderately tolerant to aminopyralid even when applied at 120 g ha(-1). The susceptibility of greenhouse-grown forbs to aminopyralid was comparable to results for the same or similar species in the field. Results from greenhouse trials could be used to predict native forb tolerance in the field.