Pamela from Charleston, Nc writes
The Rodeo Herbicide is not labeled to control duckweed so it may not work for your needs. The Diquat Water Weed and Landscape Herbicide? is labeled for duckweed control and will do a good job. For duckweed control, apply? Diquat Water Weed and Landscape Herbicide? at 1-2 gallons/A + 32 oz./A of surfactant in at least 100 gallons of water. Treatment of dense weed areas may result in oxygen loss from decomposition of dead weeds. This loss of oxygen may cause fish suffocation. Therefore, treat only 1/3 to ½ of the water body area at one time and wait 14 days between treatments.
Answer last updated on: 05/18/2018