Well, digging , and the soaking are probably your best bet, at this point, I suppose. When you get 'em dug, do some 'surgery', to expose the worm, if you can. Generally, there will only be one borer in the rhizome, as they are cannibles.....and only the strong survive!.......because, if he's INSIDE the rhizome, soaking won't be able to get to him. Their "entrance" point is inside the leaf fan, and they don't exit until they are ready to pupate.
