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

Canada Thistle Risk Assessment


Canada Thistle Plant, photo by MDA
Canada Thistle, photo by Minnesota Department of Agriculture

Common Name: Canada Thistle
Latin Name: Cirsium arvense (L.) Scop.

Reviewer: Roger Becker
Affiliation/Organization: University of Minnesota

Date: 08/16/2013
FILE #: MDARA00034CANT_2_24_2014

Final Results of Risk Assessment

Review Entity | Outcome

  • NWAC Listing Subcommittee: Restricted Noxious Weed
    Comments: First review – 06/20/2013, Final Review 08/12/2013
    The general consensus of the subcommittee based on the risk assessment data and the widespread nature of Canada thistle, was to reclassify this species as a Restricted Noxious Weed.
  • NWAC Full-group: Voted 8 – 4  to recommend reclassifying Canada thistle as a Restricted Noxious Weed.
    Comments: Review 12/18/2014 – Members agree unanimously that Canada thistle is widespread and has been a large focus of weed management for over a century in MN. However, a difference in opinion arises when the discussion centers on whether or not current efforts have any impact on controlling or eradicating populations. Some members expressed concerns that the risk assessment is ignoring the fact that without the century-long battle against this plant by counties and townships, this species would be worse today.
  • MDA Commissioner: The commissioner rejected NWAC’s recommendation and has directed that  Canada thistle remain as a Prohibited-Control species to support the counties' and townships' opinions, in addition to comments from the Farmer’s Union and MN Crop Improvement Association, that any changes would be detrimental to grazing agriculture and potentially cause confusion within the seed industry.
    Comments: Reviewed 02/24/2014 - Petition letters received by the commissioner’s office from four member organizations overwhelmingly disagreed with NWAC’s final recommendations for Canada thistle. Counties and townships also reflected the displeasure their constituents had with the notion of reclassifying this species from an enforcement perspective. They also indicated that their constituents and citizens consider this to be one of the most important weed species statewide. The MDA also received other comments regarding the recommendations to reclassify Canada thistle that basically reflected that farmers and private landowners alike would be upset if the recommendation was approved.

 

Box Question Answer Outcome
1 Is the plant species or genotype non-native? Yes (Slotta et al., 2010). Go to Box 3.
3 Is the plant species, or a related species, documented as being a problem elsewhere? Yes, in the northern hemisphere world-wide (Donald, W. 1994). It is a US Federal Noxious Weed, and is declared a noxious weed in 33 states (PLANTS database, Accessed 8/16/13). Go to Box 6.
6 Does the plant species have the capacity to establish and survive in Minnesota?    
6A Is the plant, or a close relative, currently established in Minnesota? Yes. U of M Herbarium records show the first specimen from Minneapolis in 1878. Maps show distribution throughout the US in 43 states and all but 2 Canadian Provinces (USDA Plants) and in every county in Minnesota (EDDMapS). Go to Box 7.
7 Does the plant species have the potential to reproduce and spread in Minnesota?    
7A Does the plant reproduce by asexual/vegetative means? Yes (Moore 1975). Go to Box 7B.
7B Are the asexual propagules effectively dispersed to new areas? Yes. Go to Box 7F.
7C Does the plant produce large amounts of viable, cold-hardy seeds? Yes (Becker et al., 2008). Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
7F Are sexual propagules – viable seeds – effectively dispersed to new areas? Yes, by various vectors such as on equipment, in mulch and hay, in feed and seed, etc. However, wind dispersal attached to pappi is minimal.(Becker et al., 2008). Go to Box 7I.
7G Can the species hybridize with native species (or other introduced species) and produce viable seed and fertile offspring in the absence of human intervention? No. Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
 7I Do natural controls exist, species native to Minnesota, that are documented to effectively prevent the spread of the plant in question? Not presently. There is a long history of biological control efforts on Canada thistle (McClay 2002), which have resulted in some elements of control with insects and pathogens but currently none effectively prevent spread on a broad geographical basis. Ceutorhynchus litura (F.) (synonym Hadroplontus litura) may provide significant reductions of Canada thistle in Minnesota with augmented release, but has yet to be widely accepted as host specific (personal observations) nor have wide-spread efforts been made to implement C. litura in Minnesota. (personal communication, Monika Chandler MDA). Go to Box 8.
8 Does the plant species pose significant human or livestock concerns or have the potential to significantly harm agricultural production, native ecosystems, or managed landscapes?    
 8A Does the plant have toxic qualities, or other detrimental qualities, that pose a significant risk to livestock, wildlife, or people? No known plant toxins. Physical deterrent; spines on leaves of some biotypes are fairly rigid and pose a risk to foraging animals when mature and in wide-spread, vigorous populations. Go to Box 9.
 8B Does, or could, the plant cause significant financial losses associated with decreased yields, reduced crop quality, or increased production costs? Yes (Ziska, L. 2010; Bork, et al., 2007; Grekul, C.W. and E.W. Bork. 2004; Donald and Khan, 1996). Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
 8C Can the plant aggressively displace native species through competition (including allelopathic effects)? Debatable. Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
 8D Can the plant hybridize with native species resulting in a modified gene pool and potentially negative impacts on native populations? No. Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
 8F Does the plant have the potential to introduce or harbor another pest or serve as an alternate host? No. Bold/italic text is provided as additional information not directed through the decision tree process for this particular risk assessment.
9 Does the plant species have clearly defined benefits that outweigh associated negative impacts?    
 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 (see Box 6A). Go to Box 10B.
 10B Does the plant pose a serious human health threat? No (though can be a physical deterrent, see Box 8A). 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? No, not on a statewide basis (self-evident in distribution maps and history in the state). Yes, at the local, field-specific level (Bork et al., 2007; De Bruijn, S.L. and Bork, E.W. 2006; numerous others). List as Restricted Noxious Weed. If effective biological control programs could be developed in Minnesota, then list as a Prohibited/ Control Noxious Weed

 

References:

Becker, R.L., M.J. Haar, B.D. Kinkaid, L.D., Klossner, and F. Forcella. Production and Wind Dispersal of Canada Thistle (Cirsium arvense L.) Achenes. 2008. MN DOT Report #: 2008-39.

Bork, E.W., C.W. Grekul, and S.L. DeBruijn. 2007. Extended pasture forage sward responses to Canada thistle (Cirsium arvense) control using herbicides and fertilization. Crop Protection 26(10): 1546-1555.

De Bruijn, S.L. and E.W. Bork. 2006. Biological control of Canada thistle in temperate pastures using high density rotational cattle grazing. Biological Control: Theory and Application in Pest Management. 36(3): 305-315.

Donald, W.W. (1994). The biology of Canada thistle (Cirsium arvense). Reviews of Weed Sci. 6:77-101.

EDDMapS. 2013. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Accessed August 16, 2013.

McClay, A. 2002. Canada thistle. pgs. 217- 228. In Van Driesche, R., B. Blossey, M. Hoddle, S. Lyon, and R. Reardon. 2002. Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04, 413 p.

Moore, R.J. 1975. The biology of Canadian weeds. 13. Cirsium arvense (L.) Scop. Canadian J. Plant Sci. 55:1033-1048.

Slotta, T.A.B., M.E. Foley, S. Chao, R.A. Hufbauer, and D.P. Horvath. 2010. Assessing genetic diversity of Canada thistle (Cirsium arvense) in North America with microsatellites.  Weed Sci. 58(4): 387-394.

University of Minnesota Herbarium – Bell Museum. Accessed August 8, 2013.

USDA, NRCS. 2013. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA. Accessed August 8, 2013.

 

Additional Literature:

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