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Home > Plants, Pests & Pest Control > Pest Management > Noxious & Invasive Weed Program > NWAC > Risk Assessments > Meadow Knapweed

Meadow Knapweed Risk Assessment


Common Name: Meadow Knapweed
Latin Name: Centaurea x moncktonii, C. jacea x nigra, C. pratensis Thuill, and C. debauxii subsp. Thuilleri

Reviewer: Monika Chandler
Affiliation/Organization: Minnesota Department of Agriculture

File #: MDARA00018MEDKNW_1_18_2013
Date: 09/12/12

Meadow knapweed is native to Europe and is likely a fertile hybrid between black (C. nigra L.) and brown (C. jacea L.) knapweeds (Wilson and Randall 2003). Both black and brown knapweeds are tetraploids and can hybridize freely. Hybrid offspring are also tetraploid and can backcross with either parent so population structure can be highly variable (Talbot Roché et al. 2003).

Meadow knapweed is an herbaceous perennial that occurs in cool, moist, and sunny habitats.

Meadow knapweed may have been introduced to western North America for forage, but it is not palatable and has low nutritional value. Meadow knapweed escaped cultivation and is proliferating rapidly in the Pacific Northwest. Meadow knapweed was documented recently in N. Carolina in 2011 in Allegany and Ashe Counties (Poindexter et al. 2011). It was also documented in Virginia in 2011 (Weiboldt et al. 2011). Few meadow knapweed populations have been detected in Minnesota, but infestation pockets range over large areas.

Final Results of Risk Assessment

Review Entity | Outcome

NWAC Listing Subcommittee: Suggest regulation as a prohibited noxious weed. Have to decide whether to place on eradicate or control list; or whether to combine all knapweeds.
Subcommittee debated 2 options: 1. List as a prohibited eradicate with brown knapweed due to small distributions in state. 2. Combine meadow and brown knapweeds with spotted knapweed as a prohibited-control knapweed complex - this would be done because it is hard to distinguish between the knapweed species and they can hybridize.

NWAC Full-group: List as a Prohibited – Eradicate Noxious Weed.

MDA Commissioner: Approved as a Prohibited – Eradicate Noxious Weed – 1/14/2013.

 

Box Question Answer Outcome
1 Is the plant species or genotype non-native? Yes, meadow knapweed is native to Europe (Wilson and Randall 2003). Go to Box 3.
3 Is the plant species, or a related species, documented as being a problem elsewhere? Yes.
  1. Oregon Department of Agriculture lists meadow knapweed as a Class B (weed of economic importance which is regionally abundant, but which may have limited distribution in some counties).
  2. Idaho Department of Agriculture lists it as a noxious weed.
  3. Colorado Department of Agriculture lists it as a “List A” noxious weed requiring eradication wherever found in the state.
  4. Washington Department of Agriculture lists it as a “Class B” noxious weed. Class B = Species are designated for control in regions where they are not yet widespread. Preventing new infestations in these areas is a high priority. In regions where a Class B species is already abundant, control is decided at the local level, with containment as the primary goal.
Go to Box 6.
6 Does the plant species have the capacity to establish and survive in Minnesota? Yes. Go to Box 7
6A Is the plant, or a close relative, currently established in Minnesota? There are documented infestations in St. Louis and Koochiching Counties (see map). University of Minnesota botanists documented subtypes.  
7 Does the plant species have the potential to reproduce and spread in Minnesota? Yes.  
7A Does the plant reproduce by asexual/vegetative means? Yes, propagation can be by the root crown. (Wilson and Randall 2003) Go to Box 7B.
7B Are the asexual propagules effectively dispersed to new areas? No, vegetative propagules can be dispersed on machinery, but spread by seed is more likely. (Talbot Roché et al. 2003) Go to Box 7C.
7C Does the plant produce large amounts of viable, cold-hardy seeds? Yes. (Wilson and Randall 2003) Go to Box 7F.
7F Are sexual propagules – viable seeds – effectively dispersed to new areas? Yes. Go to Box 7I.
7I Do natural controls exist, species native to Minnesota, that are documented to effectively prevent the spread of the plant in question? No. Go to Box 8.
8 Does the plant species pose significant human or livestock concerns or has the potential to significantly harm agricultural production, native ecosystems, or managed landscapes? Yes, meadow knapweed can form a monoculture reducing hay and pasture forage production (Talbot Roché et al. 2003). Wet meadows and other natural areas can also be overtaken. Centaurea x kleinii is a hybrid of meadow knapweed and yellow starthistle and was documented in Oregon. This hybrid does not occur in the native range and demonstrates the possibility of novel species of concern.(Roché and Susanna 2010) Go to Box 9.
8A Does the plant have toxic qualities, or other detrimental qualities, that pose a significant risk to livestock, wildlife, or people? Not toxic. Go to Box 8B.
8B Does, or could, the plant cause significant financial losses associated with decreased yields, reduced crop quality, or increased production costs? Yes. Go to Box 9.
8C Can the plant aggressively displace native species through competition (including allelopathic effects)? Yes. Go to Box 9.
9 Does the plant species have clearly defined benefits that outweigh associated negative impacts? No. Go to Box 10.
9A Is the plant currently being used or produced and/or sold in Minnesota or native to Minnesota? No. Go to Box 10.
10 Should the plant species be enforced as a noxious weed to prevent introduction &/or dispersal; designate as prohibited or restricted?    
10A Is the plant currently established in Minnesota? Yes, there are established populations in St. Louis and Koochiching Counties. Go to Box 10B.
10B Does the plant pose a serious human health threat? No. Go to Box 10C.
10C Can the plant be reliably eradicated (entire plant) or controlled (top growth only to prevent pollen dispersal and seed production as appropriate) on a statewide basis using existing practices and available resources? Yes, plants can be controlled with herbicides. Herbicide recommendations are similar to spotted knapweed recommendations. It is difficult to say whether statewide eradication is feasible. List as a prohibited/eradicate or control noxious weed depending on whether eradication is possible and reasonable.

References:

Poindexter, D.B., A.S. Weakley, and M.W. Denslow. 2011. New exotic additions and other noteworthy records for the flora of North Carolina. Phytoneuron 42: 1–14.

Roché, C.T. and B.F. Roché, Jr. 1991. Meadow knapweed invasion in the Pacific Northwest, U.S.A., and British Columbia, Canada. Northwest Science. 65(1): 53-61.

Roché, C.T. and A. Susanna. 2010. New habitats, new menaces: Centaurea x kleinii (C. moncktonii x C. solstitialis), a new hybrid species between two alien weeds. Collectanea Botanica 29: 17-23.

Talbot Roché, C. and D.E. Johnson. 2003. Meadow Knapweed. Pacific Northwest Extension Bulletin 0566. Oregon State University, Corvallis. (Accessed 09/11/12).

Wieboldt, T.F., G.P. Fleming, C.E. Stevens, J.F. Townsend, D.M.E. Ware, and R.A.S. Wright. 2011. Digital Atlas of the Virginia Flora. Virginia Botanical Associates, Massey Herbarium, Department of Biological Sciences, Virginia Tech, Blacksburg. 14 Jan 2011.

Wilson, L.M., and C.B. Randall. 2003. Biology and Biological Control of Knapweed. USDA-Forest Service FHTET-2001-07. 2nd Edition.