|Thacker, Eric - USU|
Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 22, 2009
Publication Date: July 2, 2009
Repository URL: http://www.pprl.ars.usda.gov
Citation: Thacker, E., Ralphs, M.H., Monaco, T.A. 2009. Seeding Cool-Season Grasses to Suppress Broom Snakeweed (Gutierrezia sarothrae), Downy Brome (Bromus tectorum), and Weedy Forbs. Journal of Invasive Plant Science and Management, 2:237-246. Interpretive Summary: Broom snakeweed is an aggressive native range weed that thrives after disturbances such as overgrazing, drought, or wildfire. Snakeweed can be controlled by herbicides and prescribed burning, however managers must establish functional plant communities that will compete with snakeweed and restrict its reestablishment. The objective of this study was to compare the ability of selected introduced and native grass species and prostrate kochia to establish and persist, and to restrict reinvasion of snakeweed, downy brome and annual weeds in replicated field studies. Crested wheatgrass established well at both locations and had the greatest biomass production. Pubescent wheatgrass established well at Howell, and squirreltail established well at Nephi. These species that established well suppressed biomass of downy brome and annual grasses. Snakeweed reinvaded only the kochia treatments, in which kochia did not establish the first year. Seeded cool season grasses will likely utilize the available soil moisture and nutrient resources and prevent reinvasion of snakeweed.
Technical Abstract: Broom snakeweed is an aggressive native range weed found throughout semi-arid areas of the western U.S., and increases following disturbances such as overgrazing, drought, or wildfires. Ecologically based strategies that include controlling snakeweed and reestablishing desirable herbaceous species are needed to restore productivity and diversity to invaded areas. The objective of this study was to compare the ability of selected introduced and native grass species and prostrate kochia to prevent reinvasion of snakeweed following control. This field study was replicated at two sites (Howell and Nephi, Utah) within the sagebrush-steppe. Snakeweed and downy brome were controlled by picloram (0.25 kg/ha) and glyphosate (1.5 kg/ha). Three species of introduced grasses and a mix, and three native grasses and a mix, and prostrate kochia were seeded into 3 x 15 m plots in October 2003. Frequency and biomass of seeded species, snakeweed, downy brome, other grasses and annual forbs were measured in 2004, 2005 and 2008. Seeded species were evaluated for success of establishment and persistence, and their ability to restrict reinvasion of snakeweed, downy brome and annual forbs. Crested and pubescent wheatgrass had the best initial establishment at Howell, and squirreltail and crested wheatgrass established best at Nephi (>90%). In contrast, kochia and Russian wildrye, did not establish well at either site, and western wheatgrass did not establish well at Nephi. Snakeweed reestablishment was restricted in all treatments except the kochia treatments, where kochia did not establish well. Frequency of downy brome increased at both sites, and annual forbs increased at Nephi to near 100%, but the better established grasses suppressed biomass production of these weedy species. Crested wheatgrass established best, had the greatest production, and provided greatest suppression of downy brome and annual weeds.