It looks a lot like spotted knapweed.
Check out
Species List
It's the Dow Chemical web site. They make Grazon P+D but their recommendation is to use Tordon 22K (1 to 1-1/2 pts per acre) or Redeem (2-1/2 to 3 pts per acre). I doubt that you will be able to get Grazon without a licence and I can't remember if one is needed for Redeem or Tordon. I haven't used either so I don't know how effective they are but usually Dow's chemicals are pretty good, expensive but good.
It looks as if you will be fighting this weed for a while so it might be benificial to get your private applicators licence. It gives you access to all kinds of good stuff. Good luck, it's a never ending fight.