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Canada thistle

Managing Canada thistle


Canada Thistle

Control: Canada thistle is difficult to control due to its extensive root system and stored nutrients which allow the plant recover from any one control method. The key to controlling Canada thistle is to combine control methods in order to stress the plant and force it to use nutrients stored in its root system. A sound management plan must be developed to implement over several years to realize success.

Chemical: Herbicides should be applied in late-springs/early summer and again in the fall. Herbicides that are recommended for use on Canada thistle, either independently or in combination, are: picloram(Tordon 22K), clopyralid(Stinger, Transline), clopyralid plus 2,4-D(Curtail), chlorsulfuron(Telar), chlorsulfuron methyl(Escort), glyphosate(Roundup, Rodeo), and dicamba(Banvel). Always read and follow label instructions when making any application. Consult your local pesticide dealer, County Weed Supervisor, or Extension Agent for specific recommendations.

Mechanical: Mowing is recommended for Canada thistle during the summer prior to seed set and repeated 2 to 3 times. Since Canada thistle is a deep-rooted perennial, hand-pulling is not very effective.

Canada Thistle

Biological: Grazing by livestock will stress Canada thistle and allow it to be more susceptible to herbicides in the fall. Grazing alone will slightly or moderately reduce root mass. The weeds must be grazed with the goal of preventing tall growth. A rotational grazing pattern should be used so as to not overgraze the desirable forbs or grasses on a site. An overgrazed site will favor Canada thistle infestation spread.


Canada thistle management calendar

  Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
Active Growth       X X X X X X X    
Bio-Control (Grazing)         X X            
Mowing             X X        
Herbicide Application         X X     X X    



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