billewing,

I too had a duckweed problem in my 1/2 acre pond. Nutrient levels were high from runoff and sediment. Went out of town for a few days and when I got back 40% of the pond was covered. My son and I built a "skimmer" out of 4" drain pipe and shade cloth. It took us about 4 hours to remove most of it. We put it in the compost pile. This seemed to be the safest with the least impact on the environment.

We still get some but not near as much as before. My guess is there are fewer nutrients in the water so the duckweed doesn't populate as fast. We now spot treat (with a 1 gallon sprayer) with Reward every 2- 3 weeks. Good luck.