Canada thistle is one of the most difficult to control weeds on Conservation Reserve Program (CRP) land and in pastures. Ten different herbicide programs were seen in side-by-side plots at a tour conducted by Iowa State University Extension at the Wendell Simonson Memorial shotgun range, SW of Swisher, on May 22, 2007. The herbicides in this trial were applied Spring 2006. Check out the Canada Thistle Results & Fact Sheet.
The best time to spray many herbicides on Canada thistle is in late spring, just before buds appear on the plants, according to Jim Fawcett, ISU Extension Crop Specialist. This usually is in late May or early June. For more information, contact the Johnson County Extension Office at 319-337-2145.
5/19/2008