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
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.