• Integrating 2,4-D and sheep grazing to rehabilitate spotted knapweed infestations

      Sheley, Roger L.; Jacobs, James S.; Martin, John M. (Society for Range Management, 2004-07-01)
      Effective integrated weed management requires understanding the impacts of management strategies applied alone and in combination. The objectives of this study were to determine the effects of 2,4-D and repeated sheep (Ovis aries) grazing applied alone and in combination on spotted knapweed (Centaurea maculosa Lam.) and perennial grasses. We hypothesized that integrating a single spring 2,4-D application would remove the adult plants, repeated sheep grazing would control rosettes, and spotted knapweed density, cover and biomass would decrease, allowing residual grasses to reoccupy the sites. A single spring 2,4-D application at 2.1 kg a.iha-1, repeated annual sheep grazing of 95% spotted knapweed or 60% grass utilization, and repeated sheep grazing and 2,4-D combined were applied to small pastures at 2 sites in western Montana beginning in 1997 and continued through 2001. Spotted knapweed rosette and flowering plant density, and spotted knapweed and perennial grass cover and biomass were sampled from 1998 through 2001. Spotted knapweed rosette density was 61.7, 34.3, 44.3, and 0.3 m-2 in the control, sheep grazing, 2,4-D, and combined sheep grazing and 2,4-D treatments, respectively, at 1 site in 2001. Spotted knapweed flowering plant density increased from 3.7 in 1998 to 10.7 m-2 in 2002 in the 2,4-D treatment whereas there was no increase in the 2,4-D combined with sheep grazing treatment from 1998 to 2002. Perennial grass biomass was 6.9, 8.4, 25.7, and 19.7 in the control, sheep grazing, 2,4-D, and combined sheep grazing and 2,4-D treatments, respectively, averaged for both sites and 4 years of sampling. Herbicides released perennial grasses from weed competition and changed the weed population from mature, less palatable plants to juvenile plants that were preferred by sheep.
    • Prescribed fire effects on dalmatian toadflax

      Jacobs, James S.; Sheley, Roger L. (Society for Range Management, 2003-03-01)
      Prescribed fires are important for rangeland restoration and affect plant community composition and species interactions. Many rangeland plant communities have been, or are under the threat of noxious weed invasion, however there is little information on how fire effects weeds. Our objective was to determine the effects of prescribed rangeland fire on dalmatian toadflax [Linaria dalmatica (L.) Miller] density, cover, biomass, and seed production. These plant characteristics, as well as density, cover, and biomass of perennial grasses and forbs were measured within burned and adjacent not-burned areas on 3 Artemisia tridentata/Agropyron spicatum habitat types in Montana. Areas were burned in the spring and measured in the fall 1999. Comparisons of plant characteristics between the burned and not-burned sites were made using t-tests and non-parametric Wilcoxon Rank Sum tests. After 1 growing season, fire did not affect density or cover of dalmatian toadflax. Burning increased dalmatian toadflax bio- mass per square meter at 2 sites, and per plant biomass at all 3 sites. Seed production of dalmatian toadflax was increased by fire at all 3 sites. Fire reduced forb cover at 1 site and increased grass biomass at 2 sites. The increases in dalmatian toadflax biomass and seed production suggest that fire used to restore healthy plant communities may increase dalmatian toadflax dominance. We recommend weed management procedures, such as herbicide control and seeding desirable species, be integrated with prescribed fire where dalmatian toadflax is present in the plant community.