Ron,
There was a news segment on Fox the other day about your Yellow Star-Thistle.
That stuff is even tougher than what you've said.
Fire can not destroy the seeds and the seeds can survive 5-10 years.Roots can go down 6 feet.
Looks like you need to bring in some weevils,fruit flys and fungus to fight it.
Three species of weevil in the beetle subfamily Cleoninae effectively reduce seed production in the yellow starthistle.
Yellow starthistle bud weevil (Bangasternus orientalis) is a fuzzy brown weevil that lays its eggs in the flowers, and when its larvae hatch, they feed on the developing seed.
Yellow starthistle hairy weevil (Eustenopus villosus) is a long-snouted, hairy-looking weevil that lays a single egg inside each flower bud. The larva then consumes the seeds within.
Yellow starthistle flower weevil (Larinus curtus) is a brownish weevil that lays eggs in the flowers as it feeds on the pollen. The larvae then eat the seeds when they hatch.
Three species of tephritid fruit fly also attack the seedheads of yellow starthistle.
Yellow starthistle peacock fly and false peacock fly (Chaetorellia australis and C. succinea, respectively) are small nectar-feeding flies that deposit eggs into the seedheads, where their larvae consume the seeds and flower ovaries.
Banded yellow starthistle gall fly (Urophora sirunaseva) produces larvae that pupate within a woody gall within the flower and disrupt seed production.
Additionally, a variety of the rust fungus Puccinia jaceae has shown promise as an agent against yellow starthistle. The rust causes widespread pathology in the leaves of the plant and slow its dispersal.