Sulfosulfuron effects on growth and photosynthesis of 15 range grasses

We conducted greenhouse experiments to compare photosynthetic and growth responses of 2 invasive annual grasses (downy brome = Bromus tectorum L. and medusahead = Taeniatherum caput-medusae (L.) [Nevski]), 6 caespitose grasses, and 7 rhizomatous grasses to the herbicide sulfosulfuron (1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea). Our objectives were to identify general patterns of species responsiveness and test the hypothesis that sulfosulfuron induced reduction in photosynthetic activity and shoot growth would be more pronounced in small relative to larger plants. Small plants in a spring experiment and large plants in a summer experiment were treated with sulfosulfuron (70 g ai ha). Wildryes and bromes were consistently injured; whereas, 5 of the 7 wheatgrasses were not susceptible to sulfosulfuron. Rhizomatous grasses generally experienced greater damage from sulfosulfuron than caespitose grasses. These results suggest that sulfosulfuron would provide a useful rangeland management tool to control unwanted invasive annual grasses without significantly hindering growth and physiology of desirable rangeland grasses.