cattails

I want to kill all of them, when and how is the best? I have three ponds 1/2 acre , 3/8 acre and a 2.7 acre.

Disc around the pond then burn 'em. You'll have quite a fire.

Use Touchdown Pro or Rodeo(Glyphosate). Its getting a little too late now to spray but you can try it out. Always spray in the fall to kill the Rhizome.

If you burn them and ice gets over the plants then it will kill the roots.

a friend of mine cuts the tails off, that seems to work well for him, they come back, but they don't spread.

What also worked for us was to use a weedwacker with a saw blade and cut it just below the water surface. Many would drown out and not come back but some still would. Thats why I feel herbicides do the trick. Depending on how much of a cattail stand you have will determine the regrowth.

we have a small pond that isnt deep around the edge. we pulled them up by the roots about 2 years ago and none have returned yet. not sure if this it practical for you but i worked for us.