Prior to applying any control method, it is important to determine if enough desirable plants are present to replace the Canada thistle. If desired vegetation is scarce or absent control will be of little value. Most control methods harm other plants. The resulting disturbances favor reinvasion by Canada thistle or other exotic species. It is also important to note that native thistles are present in the area, and should not be subjected to control.
Proper identification is important.
Frequent mowing over a number of years will control Canada thistle. Most studies indicate the need to mow patches of Canada thistle at least twice a year to prevent seed dispersal and reduce root reserves. Systematic monthly mowings may be necessary to prevent lateral flower bud development and to keep root reserves depleted. Tillage may be used to control Canada thistle. However, tillage may result in an increase in abundance due to the spreading of rootstocks and the creation of a disturbance.