If it's actually in a bed, I would dig it out. Slide your spade in sections about 3-4" down, just as you would if you were removing sod, making sure to get all the roots. Shake off excess soil if you can do it without dropping fragments of roots, and toss the root mass out. Once you're done, spade the bed and turn it over so that anything that's left is under8-10" of soil. Mulch, and that ought to take care of most of it. Keep an eye on it and weed out any stragglers that still show up and that ought to eradicate it.