Controlling Duckweed in Your Pond or Lake
Author: Terry Newhaven
In many lakes and medium- to large-sized ponds, duckweed can be a real problem. It grows very quickly and in as little as 48 hours, it can overtake a whole pond, blocking out the sun and making life a lot harder for the fish and other pond plants.
Duckweed is a tiny, fast-reproducing plant that floats on the surface of the water as well as beneath it. Only the coldest places are immune to this overtaking plant; duckweed thrives best in still, fresh waters.
Solutions
A popular solution, especially for large lake or pond owners, is skimming. According to Pond Boss, a magazine "Dedicated to managing private waters," in 2004, Venezuela's largest lake Maracaibo was completely overrun with duckweed. In order to keep the city's popular tourist site beautiful and clear, the government of Venezuela used public money to fund a project to remove the plant with a giant mechanical skimmer and was successful in removing more than 75% of the plant.
Now, that's all fine and dandy until you remember how quickly duckweed reproduces. Again, less than 48 hours your lake, pond or water garden is overrun again with the same tiny little plant floating just below the surface.
Rake It In
If you have a small enough pond, a skimmer/rake/ pond net should do you just fine. Venezuela was successful in mechanically removing almost all of the duckweed. If your pond is manageable enough, you should be able to remove most all of the duckweed with some sort of mechanical tool. We have a large assortment of maintenance products that can be used to remove duckweed and other vegetation from ponds.
Herbicides
Left best as a last resort because SO MUCH can go wrong, herbicides stand as a quick fix but remember a few things:
- Reproduction-duckweed reproduces a lot faster than the fastest bunny and it will be difficult to keep up with, which can mean multiple herbicide treatments in a season
- Other vegetation-if you have a pond, chances are you have other life (fish, aquatic plants, etc) that you wish to remain alive. While some herbicides have proven effective against duckweed, they can also kill other vegetation that you may want to keep.
These facts alone could deter you from attempting this without at least a talk with a professional. If not, look for fluridone and penoxsulam in herbicides, as they are excellent ingredients against duckweed. Sonar and WhiteCap are two products with fluridone that kill systematically by being absorbed into the plant, stopping its ability to complete photosynthesis and spread across your entire pond or lake. These products also result in longer term control than contact herbicides, often last a full season or more. If you're seeking a contact herbicide, products with diquat get the job done. RedWing is a great product, if this is what you seek. RedWing and other contact herbicides act very quickly to kill the targeted plant, but do not have as long of a lasting effect as fluridone, therefore can require multiple treatments in a season. Again, consultation with a professional is best.
A tip for when using RedWing or other contact herbicides...try and accumulate all of the duckweed into one area of the pond like a cove or bank. You may want to wait for a breezy day and let the wind help you out here. You could also look into one of our AquaSweeps to help push floating duckweed into a central location. Once all of the duckweed is collected in one area it is much easier to spray for and will result in less over spray and minimize the risk of damage to non-targeted plants. Plus it can help reduce the overall amount of herbicide you are putting into the water.
If you choose to be a DIY-hero with herbicides, please read and follow all label directions very carefully and make certain you understand that there may be collateral eradication. You could lose a few plants you really didn't want, so make arrangements. Also, make sure you physically remove dead matter from your pond. Dead organic matter can lead to oxygen depletion, which opens up another can of worms that doesn't get you any closer to enjoying your pond or lake. Seek professional advice and read the directions and follow them carefully.