Submitted to: Invasive Plant Science and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/3/2008
Publication Date: 1/2/2009
Citation: Thacker, E., Ralphs, M.H., Monaco, T.A. 2009. A Comparison of Inter- and Intraspecific Interference on Broom Snakeweed (Gutierrezia sarothrae) Seedling Growth. Journal of Invasive Plant Science and Management. 2(1):36-44. DOI 10.1614/PSM-08-099.1 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 grass species and prostrate kochia to restrict establishment and growth of snakeweed seedlings in potted-plant studies, and in replicated field studies. Interspecific interference from grasses caused greater mortality and reduced growth of snakeweed seedlings, compared to Intraspecific interference from snakeweed neighbors in the pot studies, or with no competition to snakeweed seedlings in the bare ground plots in the field study. Snakeweed seedlings appear to be sensitive to competition from other established plants. If cool season grasses can be established, they will likely utilize the available soil moisture and nutrient resources and prevent establishment of snakeweed seedlings.
Technical Abstract: Broom snakeweed is an aggressive native range weed found throughout semi-arid areas of the western U.S. that thrives after disturbances such as overgrazing, drought, or wildfire. The objective of this study was to compare the ability of selected grass species and prostrate kochia to restrict establishment and growth of snakeweed seedlings in potted-plant studies, and in replicated field studies within a sagebrush-steppe plant community. In the potted-plant studies, single snakeweed seedlings were grown with seedlings (Study 1) and established plants (Study 2) of three cool-season grasses (crested, pubescent and bluebunch wheatgrass), prostrate kochia, and snakeweed at increasing levels (1, 3, 5 plants / pot). Interference from Interspecific neighbors of crested wheatgrass in the Seedling trial (Study 1), and both crested and bluebulnch wheatgrass in the Established Neighbor trial (Study 2), induced greater mortality of snakeweed seedlings, and all interspecific neighbors suppressed snakeweed growth more than intraspecific (snakeweed) neighbors in the potted-plant studies. In the field (Study 3), snakeweed and cheatgrass were controlled by picloram (0.25 kg ae/ha) and glyphosate (1.5 kg ae/ha), then three native and three introduced grasses, and prostrate kochia were drill-seeded in replicated plots located at two sites in Utah in October 2003. Snakeweed seedlings were planted within interspaces in two 1-m2 plots within each treatment and a bare ground plot in fall 2004. Snakeweed mortality was greatest (73%) in crested wheatgrass plots at Howell UT, but there were no differences among seeded treatments at Nephi UT. Of the plants that survived, there was little growth of snakeweed seedlings in any of the seeded plots compared to bare ground plots. Seeded cool season grasses interfered and reduced establishment of snakeweed seedlings. Control of snakeweed and seeding to cool season grasses can promote weed resistant plant communities.