Common duckweed is a very small light green free-floating, seed bearing plant. Duckweed has 1 to 3 leaves, or fronds, of 1/16 to 1/8 inch in length. A single root (or root-hair) protrudes from each frond. Duckweeds tend to grow in dense colonies in quiet water, undisturbed by wave action. Often more than one species of duckweed will be associated together in these colonies. Duckweeds can be aggressive invaders of ponds and are often found mixed in with mosquito fern or watermeal. If colonies cover the surface of the water, then oxygen depletions and fish kills can occur. These plants should be controlled before they cover the entire surface of the pond
Duckweed colonies provide Habitat for micro invertebrates but if duckweed completely covers the surface of a pond for an extended period it will cause oxygen depletions. These colonies will also eliminate submerged plants by blocking sunlight penetration. Many kinds of ducks consume duckweed and often transport it to other bodies of water.
Herbicide Management Options:
Reward: is a liquid diquat formulation that has been effective on duckweeds. It is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plants cells that they contact.
Sonar AS: is a florid one compound and comes in a liquid formulation, and has been effective on duckweeds. This is a broad spectrum, systemic herbicide. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.
Clipper: is a flumioxazin product and comes in a water dispersible granule which must be mixed in water first and then either sprayed or injected. It is a broad spectrum, contact herbicide. Contact herbicides act quickly. Flumioxazin should be applied to actively growing plants and a surfactant will be needed if the herbicide is applied foliage of floating or emergent plants. Water pH needs to be below 8.5 or flumioxazin will rapidly degrade and lose effectiveness.
Biological Management Options:
Grass carp: Grass Carp will control duck weed. Young carp will consume duckweed or are not ideal for long term control. stocking rates to control duckweed is 20 fish per surface acre of plant biomass. In South Carolina, Triploid Grass Carp are legal and require permit by SCDNR. AMS can provide these permits for you.
Blue Tilapia: Will consume Duck Weed but are a warm water species that cannot survive in temperatures below 52 F. Therefore, Blue Tilapia usually cannot be stocked before mid-April and normally die in November or December. There are numerous reports of Blue Tilapia overwintering in mild South Carolina winters. Recommended stocking rates are 100 - 200 tilapia fingerlings per surface acre of plant biomass of mixed sex adult Bule Tilapia. Blue Tilapia is often not effective for vegetation control if the pond has a robust bass population due to intense predation. In South Carolina, stocking of Tilapia requires a permit from the South Carolina Department of Natural Resources. AMS is licensed to provide these permits for you.