Controlling Aquatic Weeds in Your Pond

“Help! My pond is covered with scum!” As summertime temperatures creep up, so do the number of calls Extension offices receive from residents concerned with nuisance weeds or algae in their pond. Fortunately, Clemson Extension has resources for pond owners to help them solve their pond woes.

That’s not algae!

That’s not algae! C. Guinn Wallover, ©2020, Clemson Extension

Duckweed, Lemna spp., can cover the surface of a pond, alarming pond owners.

Duckweed, Lemna spp., can cover the surface of a pond, alarming pond owners. C. Guinn Wallover, ©2020, Clemson Extension

The first step in managing these weeds is proper identification. Is that duckweed? Or, maybe algae? Or, something else? When in doubt, contact your local county Extension office for assistance in identifying the plants or algae you have present. Check out Tips for Taking Good Photos to Send to Your Extension Agent.

Clemson Extension recommends tackling problem plant and algae growth in ponds with an integrated management approach. Integrated management uses two or more methods of mechanical, biological, and chemical techniques to control aquatic plant growth in your pond. This reduces your reliance on a single method and makes for more effective management and control. Mechanical control can include raking, seining, and more. Biological control can include stocking your pond with fish such as tilapia to help control filamentous algae, and triploid grass carp to control submerged plants like hydrilla. Chemical control involves using aquatically-approved algaecides and herbicides specially formulated for use in aquatic systems like ponds and ditches. Be sure to use a Category 5 licensed pesticide applicator if you need assistance with chemical treatment or to treat ponds that are owned by a homeowner’s association. As always, the label is the law with any pesticide applied. The product label contains information for effective treatment and helps protect you, your pond, and downstream waterways.

Lastly, nutrients in stormwater runoff can stimulate aquatic plant growth. A successful aquatic plant management regime includes nutrient control to prevent future pond problems. Practices like soil testing before lawn and garden fertilization, encouraging the establishment of shoreline buffers, proper disposal of grass clippings, and reducing pet and livestock waste around the pond can all help.

Read on! For more information on the aquatic plant management practices mentioned here, check out:

If this document didn’t answer your questions, please contact HGIC at or 1-888-656-9988.

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