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UC Cooperative Extension Ventura County
669 County Square Dr. Suite 100
Ventura CA 93003
Phone: 805.645.1451
Fax: 805.645.1474

Office Hours
Our offices are currently closed due to the COVID-19 pandemic, and our team is telecommuting from home. We are available via phone and email. 

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Duckweed

 
Manual Control
 
Manual control involves physically removing the duckweeds or watermeal from the pond. Because of the explosive growth pattern of these small plants, few pond owners succeed in having manual removal solve their problem entirely. Best results are obtained if the owner regularly removes the duckweeds as they begin to become apparent. If attempted, it should be done on a day when wind has pushed the duckweeds to one side of the pond. Keep in mind that duckweeds thrive in protected ponds, so an owner may have to wait for a very windy day to try this. Once the duckweeds are pushed to one side, take a fine mesh dip net and start removing. Long-handled swimming pool nets work well. Remove as much as possible, and repeat the process as needed.
 
Chemical Control
 
Duckweed and watermeal can be controlled with herbicides although watermeal is much tougher to control than other duckweeds. Watermeal and duckweeds typically occur together, and the pond owner usually must plan his control based on watermeal recommendations. Chemical control is most effective if herbicides are applied early in the infestation, not once the pond has been covered with duckweeds. Regular walks around the pond can alert the owner to the first signs of duckweeds and watermeal. As always, be sure to read product labels for specific information on rates, application techniques, and safety.