The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008 - 8:40 AM
Effects of Timing of Defoliation on Spotted Knapweed Seed Production and Viability
Katie R. Benzel, Tracy K. Brewer, and Jeffrey C. Mosley. Department of Animal and Range Sciences, Montana State University, Bozeman, MT 59717
Spotted knapweed (Centaurea stoebe L.) is an invasive perennial forb which is one of the most economically destructive exotic species in the northwestern United States and southwestern Canada . Spotted knapweed forms large monocultures, which lowers plant diversity, reduces livestock and wildlife forage, and increases surface water runoff and soil erosion. It can produce 25-35 flowers/head, 60 heads/plant, and 5,000-40,000 seeds/meter2/year, and often produces new flowers after bud/flower removal during the bolting or flowering stage. Prescribed livestock grazing is an effective control method that is less expensive and more ecologically friendly than herbicides, however, research has yet to determine if new flowers produced following spring/summer bud removal produce viable seed by the end of the growing season. The purpose of this 2-year study was to determine the appropriate timing(s) or combination(s) of timings of defoliation on spotted knapweed to reduce viable seed production. This study was conducted on spotted knapweed-infested rangeland in west-central Montana . Ten spotted knapweed plants were hand-clipped for each of the following treatments: 1) 45% relative utilization of above-ground biomass when plants were in the bolting stage, 2) 100% of buds removed at late-bud/early-flowering stage, 3) 100% of flowers removed at full-flowering stage, 4) Treatment 1 + Treatment 2, 5) Treatment 1 + Treatment 3, 6) Treatment 2 + Treatment 3, 7) Treatment 1 + Treatment 2 + Treatment 3, 8) unclipped control. The number of seedheads per plant, number of seeds per plant, and percent viability of seeds were determined when seeds were in the well-developed stage, but bracts were still tightly closed, or at the killing frost, whichever occurred first. Preliminary results indicate that clipping in mid-June, mid-July, mid-August, or any combination of these timings can reduce viable seed production by >95% compared with no clipping. Final results will be presented.