How to Kill Duckweed


Duckweed is a tiny, waterborne plant that is considered invasive in many states. The plant can spread from body of water to body of water by clinging to the feathers of water foul, which is how the plant gets its name. Once duckweed finds a new body of water, the plant propagates rapidly to the point that it can completely cover a small pond in a matter of weeks. Manual control is rarely successful, because the plants will re-cover the pond if even one is missed. Instead, most pond owners kill duckweed using chemical herbicides.


Step 1

Measure out 1 gallon of diquat per surface acre of a pond, lake or other infected body of water.

Step 2

Mix one part chelated copper with two parts diquat. Chelated copper will not kill duckweed on it's own, but when combined with an herbicide that contains diquat, it makes the substance more effective.

Step 3

Mix the diquat at a rate of 50 parts water per one part diquat. Place the mixture in a chemical sprayer.

Step 4

Spray the surface of the water with the diquat mixture to distribute it over the surface of the duckweed plants.

Step 5

Apply a second spray within two weeks to fully control duckweed.


Step 1

Measure 1 ½ quarts of fluridone per acre of surface on your pond.

Step 2

Divide the herbicide in half.

Step 3

Spray half of the fluridone over the surface of the pond to distribute it over the duckweed.

Step 4

Wait 14 days to reapply fluridone. Spray the other half of the fluridone over the pond surface.

Things You'll Need

  • Herbicide containing fluridone or diquat
  • Chelated copper


  • Ohio State University: Duckweed and Watermeal: Prevention and Control
  • Texas A&M University: Common Duckweed
  • Iowa State University Extension: Duckweed

Who Can Help

  • University of Florida IFAS Extension: Biology and Control of Duckweed With Herbicides
Keywords: aquatic invasive plants, aquatic herbicides, preventing fishkill

About this Author

Tracy S. Morris has been a freelance writer since 2000. She has published two novels and numerous online articles. Her work has appeared in national magazines and newspapers, including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World."