Duckweed (Lemnoideae spp.) may appear small--each individual plant measures just 1/8 to 1/4 inch wide, according to Purdue University--but it can create a big problem to pond owners as it takes over the pond's surface. Left uncontrolled, duckweed can starve out more desirable pond vegetation and use up all the oxygen in the water. Various chemical and manual control options can help you remove and eradicate this aquatic pest.
Reduce water runoff into your pond, if applicable. Such runoff often caries fertilizer, dirt and organic matter that rapidly boost the dissolved nutrient levels in your pond, thus encouraging the growth of problematic vegetation like algae and duckweed, according to Ohio State University.
Release fish in your pond. Goldfish, grass carp and koi all eat duckweed and can help control it naturally, according to Iowa State University. There is no set rate of consumption, so results will vary widely.
Scoop out the duckweed. Mechanical pond skimmers can be employed in large ponds, though a simple scoop net will suffice in all circumstances. Purdue University recommends discarding the collected duckweed away from the pond's edges to avoid accidentally reintroducing the plants to the water. You can also place the vegetation in your compost pile.
Treat pond water with an aquatic herbicide. This is the most effective method of duckweed control, according to Purdue University. Iowa State University recommends using herbicides formulated with 2,4-dichlorophenoxyacetic acid (2,D-4), fluridone or diquat. Such herbicides can be purchased in most pond supply stores. Apply the herbicide according to its labeled guidelines, since toxicity varies widely by product.