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How do I kill Duckweed & Watermeal in my pond?

Posted by Heather Newhart on

Duckweed and watermeal are floating weeds that reproduce VERY FAST! One week you have some growing along the edges of the pond, and the next, your whole pond is covered. Besides looking HORRIBLE, having the surface completely covered by weeds can lead to a fish kill.

These weeds usually re-appear in your pond in late spring to early summer. This isn't a mere coincidence. Duckweed and watermeal go dormant and drop to the pond bottom when the water temperature drops in the fall, and then re-emerges when the temperature rises! You HAVE to treat these weeds to manage them. They will not go away on their own.

Your standard aquatic herbicide alone usually won't kill these weeds. Creating a "chemical cocktail" that includes Algae DefenseUltra Pondweed Defense, and Treatment Booster effectively controls these weeds. The ONLY TRICK is you need to kill ALL of the weeds. Leaving any living duckweed or watermeal will lead to regrowth. For 5,000 square feet Mix 32oz (1 qt) Ultra Pondweed Defense, 64 oz (2 qt) Algae Defense, 8 oz Treatment Booster, and 4 gal water. Spray directly on the weeds early of a sunny day.

It is very important to have pond aeration all the time, but ESPECIALLY when treating the pond with chemicals. As weeds die they consume oxygen from the water. Increasing oxygen levels will lower the risk of a fish kill during chemical application.

Make sure you know your pond size! Proper dosing is important. If you don't know your pond size- our experts can use our mapping software to determine the surface area of your pond.

How long will this treatment manage the weeds? This treatment will kill the current growth that you spray. If plants are left untreated they will repopulate. Also, these pesky weeds typically arrive in the pond via waterfowl. If there is a pond nearby with duckweed or watermeal, it is possible that they could be re-introduced. If any new growth is spotted, treat them immediately or remove them with a skimmer net before they have a change to multiply.

Note: Pond dye will not help control duckweed or watermeal as it does for algae or submerged weeds. 

  • Duckweed
  • watermeal
  • Green Pond
  • Weed Control

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