This article summarizes research presented as a poster--Integrated Management of Yellow Starthistle with Burning, Aminopyralid (Milestone ), and Revegetation--at the Western Society of Weed Science Annual Meeting, Reno, NV 2012 by Guy B. Kyser1, Arthur W. Hazebrook2, and Joe DiTomaso1
Yellow starthistle (Centaurea solstitialis L.) is a long-lived winter annual that was accidentally introduced to the United States in the mid-1800s. It has since become one of the most serious rangeland weeds in the western states, particularly in California where it is estimated to infest 13.8 million acres. Yellow starthistle management requires control of the current population, suppression of seed production and establishment of desirable competitive vegetation. This article focuses on effectiveness of integrating burning, Milestone herbicide applications, and revegetation to manage yellow starthistle.
A study was established at two locations at Fort Hunter Liggett (U.S. Army Training Center) in Monterey County, California in 2009. Objectives of the study were to: 1) to determine the effectiveness of burning followed by Milestone herbicide (aminopyralid) on yellow starthistle; 2) to evaluate revegetation success following Milestone herbicide application; and 3) to compare timing and planting techniques for success in revegetation seeding.
Field trials were established at two sites, "Mission" and "Back," located in valley bottom grassland within a mixed oak-foothill pine. Soils were sandy to gravelly loam in texture at an elevation of about 1,300 feet. The sites were burned in late October 2009. Following the burns, a flush of yellow starthistle seedlings emerged with the first fall rains.
Treatments included three reseeding times (in two seeding methods) crossed with three application timings of Milestone herbicide. Each site was established in a strip-plot with three replication of each treatment at each site. A native seed mix with mostly perennial grasses was planted December 9, 2009, January 11, 2010, and March 11, 2010. Seeding methods included drill seeding (15 to 20 lb/acre), broadcast seeding (12 to 17 lb/acre), and no seeding. Milestone at 3 fluid ounces per acre (fl oz/A) was applied with a CO2 backpack sprayer with a non-ionic surfactant on November 24, 2009, January 28, 2010 and March 19, 2010. Relative cover of yellow starthistle, native grasses, introduced annual grasses, legumes, native forbs and introduced forbs was collected from each subplot. Data were analyzed by analysis of variance for a strip-plot design.
Yellow starthistle control. Results of the study showed that fall burning alone resulted in 43% and 84% cover of yellow starthistle in the Mission and Back sites, respectively. Milestone at 3 fl oz/A applied in January or March reduced yellow starthistle cover to 0.3% (>99% control) or less at both sites. November applications of Milestone resulted in cover of 17% to 21%, probably because soil residual was not sufficient to control late-germinating seedlings. Reseeding did not affect starthistle cover.
Native forb and legume establishment. Native forbs and legumes generally established the strongest stands if drill-planted in December or January. Milestone application timing did not produce consistent effects across the two sites, but November applications tended to result in the strongest stands.
Native grasses established the strongest stands in December and January drill-planted strips, particularly in sub-subplots treated with Milestone at 3 fl oz/A in January.
Yellow starthistle control results with Milestone herbicide are comparable to previous timing trials with burning followed by Transline (clopyralid) herbicide application. Best control was with winter to early spring herbicide application timing. Native grasses were tolerant of Milestone herbicide and appeared to respond well to competitive release from yellow starthistle.
Results from this study indicate that properly timed burning, Milestone herbicide application, and revegetation can be integrated for yellow starthistle management. For optimum control of yellow starthistle, Milestone applications should be delayed until early January. In this study, the optimum time for planting native grasses was December through January.
1University of California, Davis, CA; 2United States Army, Fort Hunter Liggett, CA