Downy brome and medusahead are non-native, winter annual grass species that are rapidly invading rangeland communities across the western United States. Research conducted with the low use rate, sulfonylurea herbicide, rimsulfuron, has shown excellent control of downy brome and medusahead. The studies were established in rangeland sites in the western US, using a randomized complete block test design containing a minimum of three replicates. Plots sizes ranged from 10 by 30 to 50 feet and application dates ranged from late October to early December. Evaluations were made the following spring, rimsulfuron alone treatments at rates of 0.75 - 1 oz ai/A plus a surfactant provided 97-99% control of downy brome. In trials established on medusahead, rimsulfuron alone at 1 oz ai/A plus surfactant provided 91-93% control.  Treatments that included chlorsulfuron, to provide additional broadleaf weed control, did not impact control of downy brome or medusahead.   These studies indicate that late fall applications of rimsulfuron could be an excellent tool to help manage these two invasive weed pests and aid in restoring infested rangeland to productive use.  Additional trials are being conducted to establish grass plant back intervals for rimsulfuron.