A river surface covered in Duckweed.
Duckweed, known botanically as Lemna, is a tiny single untethered plant that floats on the surface of still and undisturbed waters. It propagates and spreads very quickly, serving as a shade and food source for water creatures. When present in overabundance, it can prevent the penetration of sunlight into the water below, choking off nutrient production during the day and cutting off oxygen supply to animals beneath the surface at night. Does this Spark an idea?
Manual Removal
The easiest and least costly method of controlling duckweed is by skimming, scooping and straining the plants from the water's surface. A long-handled, fine-mesh pool skimmer or pool brush rake are the best tools. Sweep the tool across the surface of the water, scooping up the duckweed and disposing of it at a distance from the site. While this can be time-consuming at first, once the plants are under control, maintenance becomes considerably easier.
Environmental Controls
Duckweed thrives in settings where there is very little agitation of the water's surface by either wind or waves. The application of wind by a large fan or waves by a motor will help kill and prevent propagation of duckweed.
As a biological control measure, you can introduce grass carp, which consume duckweed. Introducing carp must be planned appropriately and must be done where there is plenty of uncovered water surface area so the fish will not suffocate during the night when the plants are not producing oxygen.
Chemical Control
Chemically treating bodies of water is difficult because of the threat it poses to living creatures and beneficial plants in the area. There are several chemical herbicide options to explore. An example is a low-concentration application of a systemic herbicide called SONAR, the active ingredient of which is the chemical Fluridone. Fluridone acts to block duckweed from utilizing nutrients produced by photosynthesis, thus preventing its propagation. SONAR works at a low concentration in the parts per billion that is safe for animals.
Tags: water surface, where there