Common Pasture Pond Weeds

— Written By Jamie Warner
en Español

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If you are noticing green, floating material in your pasture pond during this time of year, you are not alone. Chances are this floating green mess is one of two things: duckweed or watermeal. These plants seem to disappear in the late fall, but they overwinter on the bottom waiting until the spring to resurface. Both plants reproduce quickly so it is important to take action promptly or risk de-oxygenation of the water, which leads to fish kills. These plants spread easily on the feathers of water fowl, the coats of cattle or other livestock as well as on boats, paddles and other equipment. Please refer to the bulleted list below for help identifying and treating the problem in your pond.


  • Free floating
  • 1/8 to ¼ of an inch in width
  • Roundish in shape
  • Single (hair-like) root hanging from each plant
  • Recommended Control Methods: Diquat or Fluridone
Duckweed images

Top: Duckweed spreading from the bank of a pond toward the center. Bottom: Note the roots hanging from the bottom of the plants.


  • Free floating
  • Less than 1mm in diameter
  • Rootless
  • Feels gritty when rubbed between fingers
  • Recommended Control Method: Fluridone
Watermeal image

Note the size comparison of the Duckweed and Watermeal.

For more information on these plants or any other aquatic weeds and their control, please contact your local Cooperative Extension Office. As always, when using chemicals to control weeds, make sure to follow the directions on the label and observe the fishing, swimming, and drinking restrictions.