Spray it with crossbow, leave it till next spring and it will be dead, roots and all. Crossbow won't kill the grasses. Make sure plant has plenty of foliage before spraying, use 1 qt. to 15 gallons for a 4 % solution and a good squirt of dawn dish soap or motor oil to help it stick to the shiny leaves. If you have lots scattered around you may want to use the purple dye in yor mix to be sure of what was sprayed or not sprayed.It will appear dead in a few weeks but do not mow it ! Roots take forever to die off, give it time. Good luck !