I finally got tired of fighting them year after year too and used a product called Eagre. It's $74.00 a quart from Stoney Creek Fisheries and Equipement Co. at 800-448-3873. They have a website at
www.stoneycreekequip.com I mixed it in a sprayer at the rate of 2 oz per gallon of water along with an activator (cide kick II) at the rate of 3 oz. per gallon of water. I saturated all of the cattails twice within a week. They turned yellow and started to wilt in a couple of weeks and then I used a manual weed cutter to cut them down and once they floated to shore raked them out and discarded them to prevent decomposition in the water and euthropication. I did not see any problems with the fish.
I do have a few cattails popping up from time to time but they are easy to pull out as they are new shoots. I would spray these too but now I have more desirable plants taking the place of the cattails and I don't want to kill them.
