Low-dose glyphosate does not control annual bromes in the northern Great Plains

Authors: Espeland, Erin; KILIAN, ROBERT - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2015
Publication Date: 9/28/2015
Publication URL: http://handle.nal.usda.gov/10113/61605
Citation: Espeland, E.K., Kilian, R. 2015. Low dose glyphosate does not control annual bromes in the northern Great Plains. Invasive Plant Science and Management. 8(3):334-340.

Interpretive Summary: Annual bromes such as downy brome (Bromus tectorum) and Japanese brome (Bromus japonicus) are weeds in rangelands of the Northern Great Plains. In order to determine the efficacy of blanket herbicide for control, we applied several low glyphosate dose rates (70, 140, and 210 g ha-1) to rangelands. We tested our ability to control annual bromes by conducting spraying in fall or in fall and spring and by measuring annual brome abundance and non-target species (perennial grasses, forbs) post-spraying. We found that a fall application of 210 g ha-1 reduced downy brome cover and seed bank density in the first year of our experiment. This application rate in this year increased Japanese brome. In the second year of our experiment, where fall- and fall- and spring-glyphosate applications were performed, there were no effects of herbicide on annual bromes. We found no negative nontarget effects on forb cover, abundance, or diversity. While low rates of herbicide application are cost-effective for large-scale use, we found no evidence that these low rates will control populations of annual bromes.

Technical Abstract: Annual bromes (downy brome and Japanese brome) have been shown to decrease perennial grass forage production and alter ecosystem functions in northern Great Plains rangelands. Large-scale chemical control might be a method for increasing rangeland forage production if low application rates confer cost savings. Downy brome can germinate in either fall or spring, where Japanese brome germinates mostly in the fall. While fall-application has been shown to be the most effective and least likely to impact co-occurring native species, spring germination of downy brome may reduce the efficacy of fall-only herbicide application. Our objective was to assess the impact of several low glyphosate dose rates (70, 140, and 210 g ha-1) applied to rangelands in fall or in fall and spring on annual brome abundance and nontarget species at two sites in eastern Montana over two years. We found that a fall application of 210 g ha-1 reduced downy brome cover and seed bank density in the first year of our experiment. Reductions in downy brome were mirrored by increases in Japanese brome. In the second year of our experiment, where fall- and fall- and spring-glyphosate applications were performed, there were no effects of herbicide on annual bromes. We found no negative nontarget effects on forb cover, abundance, or diversity. Blanket glyphosate application on rangelands is an unreliable method for controlling annual brome invasions in the northern Great Plains.