Diquat at 15 ounces per 0.1 surface area acre at 4 ft average death with non Ionic surfactant and 5 ounces 2--4D had 100 % kill of duck weed. This N W Arkansas stock pond was 100% covered with duck weed. The duckweed had been mechanically removed twice. Ph adjustment of water and enzyme and water chemistry were not preventing the exponential growth the Diquat was effective in 72 hours.