As said above use Triad/Spruce or Tropotox. We had a field almost as bad as that 3 years ago and Tropotox got rid of 99%
http://technical.nufarm.co.uk/documents/Herbicide/Label/Tropotox_labelinfo.pdf
http://technical.nufarm.co.uk/documents/Herbicide/Label/Tropotox_labelinfo.pdf