how to kill thistle weed
Canada thistle can be killed with either Roundup or 2,4-D weed killers. These weed killers will kill back the leaves on the plant and will kill back some of the root system. The best time to apply these weed killers is on sunny days when the temperatures are between 65 and 85 degrees F. (18-29 C.).hese weed killers will kill back the leaves on the plant and will kill back some of the root system. The best time to apply these weed killers is on sunny days when the temperatures are between 65 and 85 degrees F. (18-29 C.).