Post-Emergence Rescuegrass (Bromus catharticus) Control with Various Herbicides.

Rescuegrass (Bromus catharticus) is a problematic winter annual weed. Field research was conducted in 2015 in College Station and in 2015 and 2016 in Dallas, TX to evaluate herbicides for post-emergence rescuegrass control. In 2015, treatments in Dallas and College Station consisted of single applications of foramsulfuron (29 g ha^-1), trifloxysulfuron-sodium (28 g ha^-1), sulfosulfuron (105 g ha^-1), flazasulfuron (53 g ha^-1), metsulfuron-methyl (42 g ha^-1), thiencarbazone-methyl (23 g ha^-1) + iodosulfuron-methyl-sodium (5 g ha^-1) + dicamba (150 g ha^-1), and glyphosate (280 and 560 g ha^-1). Treatments were applied using standard small plot spray equipment and water carrier at 412 L ha^-1 in Dallas and 450 L ha^-1 in College Station on 17 March 2015 to multi-tiller stage rescuegrass. A second experiment was conducted in Dallas from 2015 to 2016, where, with the exception of glyphosate, the same treatments were applied singly on 15 December 2015 to plants in the 1 to 2-tiller stage and sequentially on 16 March and 7 April 2016 to plants in the multi-tiller stage.

In 2015 trials, a single application of trifloxysulfuron-sodium, sulfosulfuron, flazasulfuron, or glyphosate (560 g ha^-1) provided > 80% control at 4 weeks after treatment (WAT) in College Station. All other treatments provided ≤ 25% control. In Dallas, trifloxysulfuron-sodium, flazasulfuron, and thiencarbazone-methyl + iodosulfuron-methyl-sodium + dicamba controlled rescuegrass similarly but control was < 55% at 4 WAT. In the 2015-2016 trial conducted in Dallas, sequential applications of trifloxysulfuron-sodium and thiencarbazone-methyl + iodosulfuron-methyl-sodium + dicamba provided 88 and 77% control, respectively. Sequential applications of flazasulfuron and sulfosulfuron provided < 45% control while metsulfuron-methyl and foramsulfuron provided < 5% control. Sequential applications generally provided more control than single applications. When applied singly, no treatment provided > 55% control. Future research should evaluate fall applications of post-emergence herbicides in November while rescuegrass is still in the leaf stage and environmental conditions are conducive for herbicide activity.