Supplementary information has shown that repeated burning in May or June reduced thistle abundance in grasslands. It should be noted that Canada thistle showed an initial increase in abundance, followed by a notable reduction in abundance in most of these studies. A number of chemical control options exist for Canada thistle. Many herbicides are not specific to Canada thistle or may not be specifically licensed for this use. It is important to read and follow all label directions.
Numerous herbicides are now available for control of Canada thistle.
This mixture should be applied in the spring prior to flowering or in the fall when the rosettes are actively growing. Most herbicides, except Tordon, should not be applied while the plants are in a moisture stressed condition. Biological control of Canada thistle has received some attention. Over 80 native species of insects and over 50 species of animals and fungi utilize Canada thistle to some extent. A few have the potential for providing some measure of control.