Native forb response to sulfometuron methyl on medusahead-invaded rangeland in Eastern Oregon

Medusahead [Taeniatherum caput-medusae (L.) Nevski], a non-native, winter-annual grass (Poaceae), has\ud invaded rangelands throughout the western USA. Medusahead is an aggressive competitor that crowds out native plants\ud and reduces forage for wildlife and livestock. Sulfometuron methyl is a sulfonylurea herbicide used to control medusahead,\ud but its effect on non-target native forbs is largely unknown. We assessed the impact of an autumn application of\ud sulfometuron methyl on native forbs on the sagebrush/bunchgrass steppe of eastern Oregon over 3 years. We applied\ud 70 g a.i./ha (1.0 oz. a.i./acre) of sulfometuron methyl to randomly selected locations on three sites in a split-plot-in-time\ud (repeated-measures) experimental design. Three years after treatment, 6 of the 11 forb species studied had a significant\ud reduction in density (P < 0.05), with densities ranging from 3 to 60% of the pre-treatment levels. The results of this\ud study suggest that the benefit of medusahead control by sulfometuron methyl should be weighed against the damage to\ud non-target species