I have a small floating weed in my pond. I think it is duckweed, how do I know and how do I treat it?
Jason – Raleigh, NC
Duckweed can be a real nuisance if not identified and treated correctly. As it is a prolific grower it can quickly make your pond or lake look more like a golf course in a relatively short period of time. Duckweed is a small floating weed with a single root hair extending from the bottom of each individual leaf. Each green leaflet is about 1/8” of an inch in size and you should be able to fit about 5 to 10 on the tip of your finger. Duckweed can sometimes be confused with watermeal which is also a small green floating weed. Watermeal differs from duckweed in that it is much smaller and has a grainy or almost sandy feel to it if you hold it in your hands.
You can treat duckweed with two different methods. The first method is by spraying contact herbicides like Pond Logic® Pondweed Defense™ or Redwing™ directly onto the floating masses with a pressurized tank sprayer. This method typically yields fast results but tends to be a quick fix that ends up resulting in new growth reforming over just a few weeks. If you need to whip your pond into shape for a planned day or two event, then spraying your pond with a contact herbicide may be an appropriate treatment for you.
For longer lasting control of duckweed you can treat the pond with WhiteCap™ aquatic herbicide. This product works by inhibiting the plants ability to produce carotene and as a result chlorophyll is degraded by the sunlight and the weed dies. There are however a few things you will need to check before adding it to your pond to ensure a successful treatment. Most importantly, WhiteCap™ has a 30 day irrigation restriction meaning that if you water your plants or grass with your pond water you will not be able to do so for at least 30 days. Secondly, Whitecap needs to maintain a high concentration in the pond for up to 90 days. If your pond is prone to overflow or has an inlet/outlet chances are that the WhiteCap™ will rinse out of your pond to quickly making the treatment less effective. A good way to visually check your water loss is to color the water body with pond dye. Dye will typically remain in your pond for 2-4 weeks in normal conditions. If your pond looses color sooner then it is a great indicator that too much water is exiting the pond.
As WhiteCap™ is degraded by sunlight it is important that you dye your pond while you are chemically treating the water body. When applying WhiteCap™ use a pressurized tank sprayer and submerge the spray nozzle to apply the herbicide beneath the surface of the pond where it is safe from evaporation and sun exposure.
The best time to use WhiteCap™ is early in the spring a couple of weeks before you normally see duckweed forming in your pond. This will give the herbicide a chance to establish itself in the pond and discourage plant growth before it gets out of control.
Pond Talk: Have you experienced Duckweed in your pond?