I'm having good luck controlling cattails on our pond by cutting. In spring I've cut the newly emergent growth in areas where I want heavy cattail cover for wildlife nesting. The sparse plants in spots like that then produce many, many leaves and later there is great cover.

In spots where I don't want cattails, like say around my dock or at specific fishing access points, I cut the leaves below the water line during the summer. The plants brown up and the roots eventually die and pull free from the pond bottom.

In a few years more cattails will invade these bare spots, but cutting the invaders is easy. I haven't resorted to chemical treatments, as manual cutting solves my problems.

I've cut with a knife, hedge pruners, weed whacker, and even a small chain saw. Hey, I'm a retired timber feller and a practicing arborist, so why not run the Stihl or Husqvarna?

Good luck.