Centaurea stoebe is a perennial forb belonging to the family Asteraceae. Since its introduction from eastern Europe, C. stoebe has spread widely and caused substantial economic damage (Harris and Cranston, 1979, Watson and Renney 1974). As of 2000, this species had successfully invaded 7.5 million acres of North American land; it was present in 46 states as of 2019 (USDA 2019, Zouhar 2001).
Many studies have attempted to identify what makes Centaurea stoebe a successful invader. C. stoebe is highly tolerant of disturbance, thrives in a variety of soils, and can occupy multiple niches (Lacey et al. 1989, Watson and Renney 1974, Zouhar 2001). In North America, the species is almost entirely tetraploid, while both diploid and tetraploid plants are common in Europe, where it is native. The tetraploid plants expressed higher reproductive vigor and were better adapted to dry habitats than diploid plants (Treier et al. 2009). Multiple introductions to North America may have provided the tetraploid cytotype greater genetic diversity, which may have allowed stronger resistance to biocontrol species in C. stoebe’s non-native range (Marrs et al. 2010). Allelopathy was suggested to be a method by which C. stoebe competes with native plants, but this hypothesis has been challenged (Blair et al. 2005, Locken and Kelsey 1967, Ridenour and Callaway 2001).
Centaurea stoebe’s ability to compete with other plants and alter its environment has been shown to cause a reduction in native plant and bird diversity (Lesica and Shelley 1996, Ortega et al. 2006, Tyser 1990, USFWS 2014, USFWS 2001). C. stoebe has threatened multiple endangered species (Figure 1). C. stoebe has been found to increase runoff and sedimentation rates, which threaten the health of nearby aquatic habitats, increases soil erosion, and can result in further invasion (Lacey et al.1989).
Figure 1. Table of endangered species known to have been threatened by Centaurea stoebe. Species are listed by common name, organism type, and how this species is threatened by C. stoebe.
|Endangered Species||Type||Threat by Centaurea stoebe|
|Mt. Sapphire rockcress||Forb||Direct competition, habitat loss and degradation (cryptogamic crust)|
|Spalding’s catchfly||Forb||Direct competition|
|Gunnison sage-grouse||Bird||Habitat degradation and loss|
Biological control has been identified as the most economical method of managing C. stoebe populations, but was more likely to limit a populations’ spread than to eradicate the species (Carson et al. 2014, Harris and Cranston 1979, Knochel and Seastedt 2009). Herbicides have been shown to reduce C. stoebe cover for a short period, but sites were recolonized as herbicide concentrations declined (Davis 1990, Knochel and Seastedt 2009). A single mowing while Centaurea stoebe was reproducing significantly reduced C. stoebe cover (Rinella et al. 2001). Another study found that mowing at the bolting, budding, or flowering stages increased mortality of biocontrol insects (Story et al. 2010). In any season, multiple clippings or intense clipping of native vegetation increased C. stoebe cover (Jacobs and Sheley 1999). Spring and summer burning may encourage competition from native flora and reduce Centaurea stoebe cover, though prescribed fire has also increased C. stoebe cover (MacDonald et al. 2019, MacDonald et al 2007, Pitman 2018, Smith and Arno 1999). Hand removal of individuals proved to be more effective than herbicide, mowing, or burning in an 8-year study (MacDonald et al 2019). Though labor-intensive, this treatment nearly eliminated Centaurea stoebe in the treated area.
Competition from the plant community and combining strategies often increased the effectiveness of treatments (Knochel et al. 2010, Knochel and Monson 2010, Maines et al 2013, Sheley et al. 1998). The combination of plant competition and biocontrol insects was effective in reducing C. stoebe growth and reproduction (Knochel et al. 2010, Knochel and Monson 2010). Herbicide use increased the success of grazing, prescribed burning, and biocontrol predation (Jacobs, 2012, Sheley et al. 2004, Sheley et al. 1998).
Successful management strategies varied by climate, habitat and nutrient availability of sites (Knochel and Seastedt 2009, Morodoluwa and Gurevitch 2018, Zouhar 2000). Environmental factors should be taken into consideration when planning to control or eradicate Centaurea stoebe populations.
Blair, A. C., B. D. Hanson, G. R. Brunk, R. A. Marrs, P. Westra, S. J. Nissen, and R. A. Hufbauer. 2005. New techniques and findings in the study of a candidate allelochemcial implicated in invasion success. Ecology Letters 8:1093-1047.
Carson, B., C. A. Bahlai, and D. A. Landis. 2014. Establishment, impacts, and current range of spotted knapweed (Centaurea stoebe ssp. micranthos) biological control insects in Michigan. Great Lakes Entomologist 47:129-148.
Davis, E. S. 1990. Spotted knapweed (Centaurea maculosa L.) seed longevity, chemical control, and seed morphology. M.S. Thesis, Montana State University, Bozeman, MO, USA.
Harris, P., and R. Cranston 1979. An economic evaluation of control methods for diffuse and spotted knapweed in western Canada. Canadian Journal of Plant Science 59:375-382.
Jacobs, J. S. 2012. Plant guide for spotted knapweed (Centaurea stoebe L.). United States Department of Agriculture, Natural Resources Conservation Service, Bozeman, Montana.
Knochel, D. G., C. Flag, and T. R. Seastedt. 2010. Effects of plant competition, seed predation, and nutrient limitation on seedling survivorship of spotted knapweed (Centaurea stoebe). Biological invasions 12:3771-3784.
Knochel, D. G., and N. D. Monson. 2010. Additive effects of aboveground and belowground herbivores on the dominance of spotted knapweed (Centaurea stoebe). Oecologia 164:701-712.
Knochel, D. G., and T. R. Seastedt. 2009. Sustainable control of spotted knapweed (Centaurea stoebe). In Management of invasive weeds. Springer, Berlin, pp 211-225.
Lacey, J. R., C. B. Marlow, and J. R. Lane. 1989. Influence of spotted knapweed (Centaurea maculosa) on surface water runoff and sediment yield. Weed Technology 3:627-631.
Lesica, P., and J. S. Shelley. 1996. Competitive effects of Centaurea maculosa on the population dynamics of Arabis fecunda. Bulletin of the Torrey Botanical Club 123(2):111-121.
Locken, L. J., and R. G. Kelsey. 1967. Cnicin concentrations in Centaurea maculosa, spotted knapweed. Biochemical Systematics and Ecology 15(3): 313-320.
MacDonald, N. W., B. T. Scull, and S. R. Abella. 2007. Mid-spring burning reduces spotted knapweed and increases native grasses during a Michigan experimental grassland establishment. Restoration Ecology 15(1):118-128.
MacDonald, N. W., K. M. Dykstra, and L. M. Martin. 2019. Restoration of native-dominated plant communities on a Centaurea stoebe L. – infested site. Applied Vegetation Science. Advance online publication.
Maines, A. P., D. G. Knochel, and T. R. Seastedt. 2013. Factors affecting spotted knapweed (Centaurea stoebe) seedling survival rates. Invasive Plant Science and Management. 6:568-576.
Marrs, R. A., R. Sforza, and R. A. Hufbauer. 2010. Evidence for multiple introductions of Centaurea stoebe micranthos(spotted knapweed, Asteraceae) to North America. Molecular Ecology 17:4197-4208.
Morodoluwa, A. F., and J. Gurevitch. 2018. The influence of environmental factors on the distribution and density of invasive Centaurea stoebe across Northeastern USA. Biological Invasions 20:3009-3023.
Ortega, Y. K., K. S. McKelvey, and D. L. Six. 2006. Invasion of an exotic forb impacts reproductive success and site fidelity of a migratory songbird. Oecologia 149: 340-351.
Pitman, Z. T. 2018. Effects of fire season and temperature on a spotted knapweed (Centaurea stoebe) infested grassland. M.S. Thesis, Grand Valley State University, Allendale, MI, USA.
Ridenour, W. M., and R. M. Callaway. 2001. The relative importance of allelopathy in interference: the effects of an invasive weed on a native bunchgrass. Oecologia 126:444-450.
Rinella, M. J., J. S. Jacobs, R. L. Sheley, and J. J. Borokowski. 2001. Spotted knapweed response to season and frequency of mowing. Journal of Range Management 54: 32-56.
Sheley, R. L., J. S. Jacobs, and M. F. Carpinelli. 1998. Distribution, biology, and management of diffuse knapweed (Centaurea diffusa) and spotted knapweed (Centaurea stoebe), Weed Technology 12(2): 353-362.
Sheley, R. L., J. S. Jacobs, and J. M. Martin. 2004. Integrating 2, 4-D and sheep grazing to rehabilitate spotted knapweed infestations. Range Management 57:371-375.
Smith, H. Y. and S. F. Arno, editors. 1999. Eighty-eight years of change in a managed ponderosa pine forest. General technical report RMRS-GTR-23. United States Department of Agriculture, Rocky Mountain Research Station, Ogden, Utah.
Story, J. M., J. G. Corn, and L. J. White. 2010. Compatibility of seed head biological control agents and mowing for management of spotted knapweed. Environmental Entomology. 39:164-168.
Treier, U. A., O. Broennimann, S. Normand, A. Guisan, U. Schaffner, T. Steinger, and H. Müller-Schárer. 2009. Shift in cytotype frequency and niche space in the invasive plant Centaurea maculosa. Ecology 90(5): 1366-1377.
Tyser, R. W. 1990. Ecology of fescue grasslands in Glacier National Park. In: Boyce, M.S., S. G. E. Plumb. National Park Service Research Center. 14th annual report. Laramie, WY. University of Wyoming, National Park Service Research Center: 56-60.
U.S. Fish and Wildlife Service. 2014. Threatened status for Gunnison sage-grouse. Federal Register 79: 69192-69310.
U.S. Fish and Wildlife Service. 2001. Endangered and threatened wildlife and plants; Final rule to list Silene spaldingii (Spalding’s Catchfly) as threatened. Federal Register 66: 51598-51606.
U.S. Department of Agriculture, National Resources Conservation Service. 2019. The PLANTS Database. National Plant Data Team, Greensboro, NC, USA.
Watson, A. K., A. J. Renney. 1974. Biology of Canadian weeds. 6. Centaurea diffusa and C. maculosa. Canadian Journal of Plant Science 54: 687-701.
Zouhar, K. 2001. Centaurea stoebe subsp. micranthos. In: Fire Effects Information System, [Online]. US. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Services Laboratory (Producer).