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I'd never thought about using RoundUp on cat-tails. Never researched it because I just assumed it wouldn't work. Learn something new here everyday. I know it has replaced my weedeater for the most part, much to the griping of my wife who doesn't like my band of dirt around every obstacle in the yard...
I also spray around trees. However, we have a couple highly visible ones in the front yard. With those, I put down a little weed fabric covered with bark and add a couple decorative rocks. It keeps certain people happy.
I used to have a problem with cattails plugging up an irrigation ditch. It took several applications but Roundup got rid of them.
