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