It's too late to use 24D if you want control this year. I just treated an acre pond consumed with watershield and got great control using Clipper. It will burn it out for the rest of the year but will come back next year and you can use Navigate or Rodeo. The Clipper will work in a few weeks because it is a contact herbicide where 24D is systemic and will not be able to kill the root with the remaining growing season 2011. You can buy Clipper Herbicides anywhere on the web. Just google it.