If you don't want any plants in the pond, research fluridone (Whitecap/Sonar A.S.) if you don't have water moving thru your pond (water flow in and out).

It won't be cheap, but it wipes out all the plants in the pond, duckweed/watermeal included. It's not an overnight kill, plan on 30-90 days if the concentration is kept at the proper levels.

www.hoosierpondpros.com

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).