Duckweed Control in Ponds

Reducing Nutrients

• Reducing the level of nutrients in the pond is among the preventative control strategies for duckweed. Heavy levels of nutrients in the water can lead to severe growth of duckweed. Frequent causes of nutrient in the pond include runoff from lawn fertilizers, inefficient septic tanks or excessive amount of leaves in the ponds. Ponds susceptible to runoff from agricultural fields also have problems with duckweed. Controlling nutrient levels in ponds can eliminate or reduce duckweeds the following year.

Aeration

• Ponds that are frequently aerated with bubble aerators have less problems with duckweed. Aeration reduces the amount of decomposed material on pond bottoms. The bubbles lift organic sediments from the bottom to the water surface to be readily utilized by the plankton, decreasing the nutrients that support duckweed growth. Regularly aerating ponds and reducing other unnecessary nutrient sources simultaneously in the water are effective non-chemical control of duckweed.

Natural Predators

• Introducing fish like grass carp and koi into ponds helps control duckweed as both fish feed on the plant. However, grass carp feeds on other plants as well and this can cause duckweed to build up to a level where grass carp alone may not be sufficient for control. Koi are effective when introduced into the pond in early spring before the plants reach invasive levels.

Chemicals

• Chemical control for duckweed includes the use of copper-based compounds or products containing fluridone or diquat. All chemicals are sold under different trade names and are most effective when used when the first signs of infestation occur. It takes one to three months for complete eradication of duckweed with multiple applications of fluridone and diquat.