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Invasion and ecology of spotted knapweed (Centaurea stoebe) in the continental United States: a mini review

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.




Literature Cited

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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.

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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.

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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.

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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.

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By K.T. Strain

Katie Strain is a texan, plant enthusiast, and Ph.D. student studying Evolution, Ecology and Conservation biology.

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