Floating Aquatic Weeds are loved by some and hated by others. It seems ironic, but millions of dollars are spent each year both purchasing and killing these plants. Below is a listing of some of the common types:
Duckweed (Lemna minor)
Duckweed is a true floating aquatic weed with leaves on the surface and roots extending downward, absorbing nutrients directly from the water. Common Duckweed is about the size of the end of a pencil eraser and is found throughout the USA.
Duckweed occurs in areas of still water, and can reach nuisance proportions in nutrient rich ponds that are protected from the wind. Below are listed several control techniques.
- Ultimately, the best way to control this weed is to control the nutrients reaching the pond and to increase the amount of natural wind. For information on dealing with nutrients, review the Planktonic Algae section of our Algae Control Page. Whether or not you can increase natural wind depends on the situation, but pond owners that thin heavy tree and brush lines along pond edges can see improvements.
- If you are unable to increase natural wind exposure, the best control option may be to artificially create moving water…this can be done with Surface Aerators. One of the most effective methods is to use a Kasco Deicer and Horizontal Floatation Kit to create a “stream” of water. Duckweed will not grow if the water is in motion.
- There are 2 main chemical treatment options for this weed. The first is to apply Reward, with a Surfactant and spray over the plants. These chemicals kill on contact, but usually some Duckweed will survive and regrow, which necessitates repeat treatments. A second, and more effective, option is to treat the water body with Sonar , which is a longer term systemic herbicide. The only drawback to this option is that it is likely to also kill beneficial aquatic plants, but not algae. A new product called Clipper has become available that is very effective against Duckweed.
- Triploid Grass Carp and Koi will both readily consume Duckweed, but almost always the plant reproduces faster than the fish can eat it. Therefore, we do not recommend this control option.
Watermeal (Wolffia spp.)
Watermeal is the smallest of flowering plants at the size of a grain of sand. Unfortunately, it is also among the most difficult to control. It is found throughout the United States.
Almost all of the above information that is true for Duckweed is also true for Watermeal. One major exception though is that Watermeal is only listed as “Partially Controlled” on the Sonar product labels. What this means is that most of the time these products will control Watermeal, but for whatever reason, sometimes the treatment will be ineffective. There is a new product called Clipper that is very effective against Watermeal. See the product page for more information on Clipper.
Water Hyacinth (Eichhornia crassipes)
This plant is common in tropical and sub tropical areas of the USA. Water Hyacinth grows vigorously in nutrient-rich waters with its thick black roots extending to the bottom or free floating. Flowers are bluish to white with yellow centers. It is an excellent plant for filtering water and providing fish habitat, but it can quickly take over if not managed. In fact, many noxious weed experts consider this one of the most invasive weeds in the world! Triploid Grass Carp and Koi may nibble at this plant, but they will not control it. The best chemical control options is to spray with Reward, and a Surfactant, or spray with a mix of Shore-Klear or AquaNeat and a Surfactant.
Water Lettuce (Pistia stratoites)
Found in the extreme Southeastern USA, this plant is very sensitive to frost. Water Lettuce has lime-green leaves with deep veins radiating outward from the base. Roots dangle into the water, making it a true floating plant, and it prefers quiet, partially shaded, nutrient-rich waters to grow. Triploid Grass Carp and Koi will nibble at this plant, but they usually will not control it. The chemical method of choice is to spray plants with Reward and a Surfactant.
Water Lilies & Spatterdock
Common Water Lilies of the USA include the Yellow Water Lily (Nuphar spp.), a.k.a. Spatterdock, and the ever popular White Water Lily (Nymphaea spp.). The common native species of White Water Lilies usually have a white blossom and large, round, cleft leaves that are 6 to 12 inches in diameter and purplish-red on the underside, but the decorative cultivars come in a myriad of colors and patterns. They can provide terrific fish and wildlife habitat, but in certain favorable conditions they can spread and cause problems. In those instances, the best chemical treatment is spot treating with Navigate, a 2,4-D product, before blossoms develop, or spraying pads with a mixture of Shore-Klear or AquaNeat and a Surfactant. See the Product Selection Chart for alternative treatments.