I use a product known as Eagre mixed 2 oz. per gallon of water and another 3 oz. of an activator such as Cide Kick II. I mix well and spray in a manual pressurized tank.
It may require up to 2 applications, and I go one step further. Once the cattails turn yellow and start to wilt, (you should wait that long to make sure the chemical gets to the roots), I cut them down with a weed cutter as close to the bases as possible, allow them to float to shore, and remove them with a rake. This prevents decomposition of the plants adding to organic load.
I now have very few cattails sprouting and any that do, I either pull by the roots and all, or douse a rag with the preceding herbicide and rub it on the cattail. This is due to the fact that some more desirable plants i.e. bullrushs may be very close to the new cattail shoot and I don't want to kill them from overspray. I am seeing bullrush over take shallow areas once proliferated with cattails, but the bullrushes do not grow as deeply or as high.
Weedtrine is not indicated for cattails! I have not seen a toxic effects or any effects on my fish using Eagre. I believe Rodeo may be a similar product but don't quote me.
