General Impact
Nuzzo (1997) states that C. arvense threatens natural communities by directly competing with and displacing native vegetation, decreasing species diversity, and changing the structure and composition of some habitats. Species diversity in an "undisturbed" Colorado grassland was inversely proportional to the relative frequency of C. arvense. It presents an economic threat to farmers and ranchers. Infestations reduce crop yield through competition for water, nutrients and minerals, and through interference with harvest. In Canada, the major impact of C. arvense is in agricultural land, and in natural areas that have been disturbed or are undergoing restoration. In the United States, it is a host for bean aphid and stalk borer, insects that affect corn and tomatoes, and for sod-web worm, which damages corn. In Bulgaria, C. arvense is a host for the cucumber mosaic virus. In addition to reducing forage and pasture production, it may scratch grazing animals, resulting in small infections. Zouhar (2001) reports that it has been identified as a management problem in many national parks and on TNC (The Nature Conservancy) preserves in the upper Midwest, the Great Plains states, and the Pacific Northwest. Infestations of C. arvense may contribute to the elimination of endangered and/or endemic plant species, such as the Colorado butterfly plant in Wyoming.
Location Specific Impacts:Canada 
Agricultural: Zouhar (2001) states that it is considered one of the most tenacious and economically important agricultural weeds. Nuzzo (2001) states that infestations reduce crop yield through competition for water, nutrients and minerals, and through interference with harvest. In Canada, the major impact is on agricultural land and in natural areas that have been disturbed or are undergoing restoration. United States (USA)
Agricultural: Thunhorst and Swearingen (1997) report that Cirsium arvense has long been recognized as a major agricultural pest. Nuzzo (2001) states that infestations reduce crop yield through competition for water, nutrients and minerals, and through interference with harvest. It is a host for bean aphid and stalk borer, insects that affect corn and tomatoes, and for sod-web worm (Crampus sp.), which damages corn.
Competition: It threatens natural communities by directly competing with and displacing native vegetation, decreasing species diversity, and changing the structure and composition of some habitats (Nuzzo, 1997).
Economic/Livelihoods: Zouhar (2001) states that it is considered one of the most tenacious and economically important agricultural weeds. It presents an economic threat to farmers and ranchers (Nuzzo, 1997), costing tens of millions of dollars in direct crop losses annually and additional millions for control (Thunhorst and Swearingen, 1997). Wyoming (United States (USA))
Other: Infestations of Cirsium arvense may contribute to the elimination of endangered and/or endemic plant species such as the Colorado butterfly plant in Wyoming (Zouhar, 2001).
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