Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2008
Publication Date: 1/1/2009
Citation: Ralphs, M.H. 2009. Response of Broom Snakeweed (Gutierrezia sarothrae) and Cool-Season Grasses to Defoliation. Journal of Invasive Plant Science and Management. 2(1):28-35. DOI. 10.1614/PSM-08-075.1
Interpretive Summary: Locoweeds can be controlled by rangeland herbicides, but their seedbank in the soil ensures they will reestablish when environmental conditions are favorable. The objective of this study was to control white locoweed with herbicides, then seed to cool-season grasses to determine if their greater competitive ability could suppress reestablishment of white locoweed. Crested wheatgrass, Siberian wheatgrass and Russian wildrye successfully established. Where pubescent wheatgrass established, it produced the greatest mortality of locoweed seedlings. All seeded species suppressed reestablishment of indigenous locoweed species. Forage production of seeded grasses was 2 to 3 times greater than native grasses. Seeding cool-season grasses following locoweed control can suppress locoweed reestablishment and increase forage production in spring when locoweed is the greatest threat to livestock.
Technical Abstract: Livestock poisoning can occur on short-grass prairies when locoweeds (Astragalus and Oxytropis spp.) are actively growing in spring before warm-season grasses begin growth. White locoweed grows in early spring, completes flowering and seed production by early summer, and goes dormant. Perennial cool-season grasses may provide competition to suppress locoweed or reduce in reestablishment following control. Furthermore, these grasses may provide alternative palatable forage to livestock early in the spring. The objective of this study was to suppress white locoweed reinvasion by seeding cool-season grasses at two mixed-grass and two short-grass prairie sties. White locoweed and associated species were controlled with glyphosate (1.1 kg ae/ha) and picloram (0.38 kg ae/ha) in 3 by 15 m plots. The plots were seeded to “CDII” crested wheatgrass, “Vavilov” Siberian wheatgrass, “Luna” pubescent wheatgrass, “Bozoisky” Russian whildrye, smooth brome, “NewHy” wheatgrass, sideoats grama, and “Immigrant” forage Kochia. In addition, a native grass plot, treated with picloram to control locoweed without harming the native grasses, and a nontreated control plot, were established in each replication. Establishment of crested wheatgrass, Siberian wheatgrass, and Russian wildrye averaged 60% over all sites. The other treatments had establishment rates < 30% and were considered unsuccessful. Forage production of Russian wildrye was 2,962 kg/ha, Siberian wheatgrass was 2,736 kg/ha, and crested wheatgrass was 2,339 kg/ha compared with 1,051 kg/ha for nontreated control. Mortality of locoweed seedlings was greatest in the pubescent wheatgrass seeding. All seeded species suppressed reestablishment of indigenous locoweed plants.