Can you burn it?
If you can't burn it, then depending on how much thistle you have and your energy level, you could walk around with a bucket and pruners and cut off the seed heads. Sounds tedious, but the fewer seeds that are left viable in the field, the better.
Are there ANY plants that are still in the bud stage? Clopyralid3 label says thistle can be treated all the way up to the bud stage. I've had great luck killing bud-stage Canada Thistle with C3. In fact, later maturity spraying of CT may be more effective than spraying in the rosette stage.
I will say this...at least it isn't Canada Thistle in your pic.