Managing Canada Thistle (Cirsium Arvense) In A Constructed Grassland With Aminopyralid And Prescribed Fire

Green spaces such as golf courses that intermingle within or exist on fringes of urban landscapes can provide opportunities for increasing the ecological value of urban areas. To that end, more naturalistic and less input-intensive "links''-style golf courses have recently gained favor over input-intensive parkland courses. The Osgood Public Golf Course in Fargo, ND is a links-style golf course set adjacent to suburban housing developments. This course incorporated large areas of prairie plantings, or "constructed grasslands,'' which over time became dominated by fescue species and infested with Canada thistle. Our objective was to explore the efficacy of using prescribed fire combined with aminopyralid herbicide to control Canada thistle and promote a more diverse mix of warm-season C-4 and cool-season C-3 grasses. Aminopyralid was applied during fall 2010 and prescribed fire was applied during spring 2011. We found that aminopyralid provided excellent control of Canada thistle 1 and 2 yr post-treatment. Open niches created from Canada thistle control were readily filled by C-3 grasses, primarily fescue species, which were the dominant species on the constructed grasslands prior to treatment. Fire intensity was variable within and across plots and was associated with reductions of litter and C-3 grasses, but was not associated with increases of C-4 grasses within the time frame of this study. Our results demonstrate the effectiveness of aminopyralid for Canada thistle control in constructed grasslands. Prescribed fire maintained C-3 grass dominance while removing litter, but C-4 grass response was variable and appeared dependent on pretreatment C-4 species abundance. Reduction of litter in constructed grasslands dominated by fescue could potentially lead to microsite conditions that would favor C-4 and other C-3 species, especially if short-term management promoted additional facilitation efforts, such as repeat spring fire treatments and seeding.