Many people have cattails in their pond and want a safe spray to control them. There is 1 spray that can be used to safely to eliminate cattails. This spray will not harm the fish or the zooplankton. It is called "RODEO" by Mansanto. It will take probably 2 applications to effectively kill them. The plants need to be actively growing to allow the poison to be sucked into the plant. The poison travels to the roots and kills the rhisomes. If there is some overspray on the water it will not harm anything. This will kill any plant that is above the water surface. You should be able to get this product at Estes Chemical Co in OKC,Enid, or Paris Tx. You may have to explain what the chemical is designed to do as there may be a generic name for the product. Many times this is the case.
Mix according to directions and apply by pump up sprayer.