Dam covered in duckweed

Q. We have a dam that is covered in duckweed, can you help?

by Aquatic Technologies

A. Don't panic there are lots of ways to treat Duckweed

Duckweed has 1-3 oval shaped leaves, is light-green in colour, nearly flat on both sides and float on or just beneath the water’s surface. Dense growth appears as a green mat on the surface of the water.

How severe is your Duckweed bloom?
The growth stage of your Duckweed bloom will impact your treatment options.

  1. Primary Growth Stage (0-30%): early stages of infestation, crowded plants, water surface visible
  2. Secondary Growth Stage(30-60%): moderate infestation, water surface barely visible
  3. Tertiary Growth Stage(60-100%): mature infestation, water surface is not visible
  4. Multilayered Growth Stage (100% +): display ridge-like thickening as layers build up

Treatment Options

AQ200 is a chemical herbicide that will treat your Duckweed bloom regardless of its growth stage and acts quickly to kill the weed. Typically, you will see results within 1 -7 days of application.

Keep in mind there is a withholding period once the herbicide has been applied. This means the water cannot be used for either irrigation or watering stock for 10 days. This allows time for the herbicide to breakdown.

Orange Oil is a natural product that requires multiple treatments to kill free floating weeds.

This treatment is better suited for earlier stages of the weed’s bloom where the growth is single layer and water is still visible. Orange oil provides a more natural, environmentally benign option.

If you would still prefer to use orange oil on a mature bloom, you will need to physically remove enough duckweed for the water to be visible again before adding the herbicide.

It is recommended that physical removal of duckweed is used in combination with a herbicide treatment. Removal alone can mean duckweed grows back rapidly.

Physical removal can be achieved by using an aquatic surface skimmer or ordinary household items such as a rake or a bucket. This works best if you keep collected duckweed away from the water’s edge to ensure it does not return into the water body.

Habitat
Stationary and slow-moving water bodies with high levels of nutrients (nitrogen)

What are the environmental impacts of a duckweed bloom?
Having a dam covered in Duckweed can have several negative impacts on your water body;

  • it prevents oxygen diffusion
  • it prevents light reaching submerged vegetation, limiting growth and causing death
  • leads to fish and other aquatic life death
  • it can promote harmful algae and bacteria growth
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