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Azolla (Mosquito Fern)

azolla caroliniana

Azolla is a nitrogen-harboring true fern and it will multiply its weight three times each week during the summer months.

Mosquito fern is nonnative and on the federal noxious weed list and should not be grown.

Any type of this plant is not recommended to be grown if no ornamental fish are present.

Mosquito fern can be removed by raking or seining it from the pond's surface.

Azolla has several names Azolla Caroliniana or its more common names fairy moss or mosquito fern.

Azolla Caroliniana is a species of Azolla it is native to America, Argentina, and Uruguay. It is a freshwater plant aquatic fern, with scale-like frond 5-10mm long, green to reddish, most often reddish in strong light and in winter.

They are covered in fine hairs that give it the appearance of velvet. It is able to fix nitrogen from the air by means of symbiotic cyanobacteria. It can survive winter water temperatures of 5° C with optimum summer growth between 25-30° C.

Mosquito fern is of commercial importance in cultivation in southern and eastern Asia as a bio-fertilizer, valued for its nitrogen-fixing ability, which benefits crops such as rice when the fern is grown under it and reduces the need for artificial fertilizer addition. The thick mat of fronds also suppresses pond algae.

Harvested fronds are also used as a food for fish and poultry. It is also often used as a floating plant in both cold water and tropical aquariums, as well as in outdoor goldfish ponds; it is propagated by division.

Azolla prefers slightly acidic water and can be collected and transferred during the spring or summer. It is best to place mosquito ferns in sheltered areas of the pond.

Mosquito Fern Control Options


Mosquito fern can be removed by raking or seining it from the pond's surface.


Grass carp will seldom control aquatic vegetation the first year they are stocked. They will consume mosquito fern but it is not a preferred food item. Grass carp stocking rates to control mosquito fern are usually in the range of 7 to 15 per surface acre or more.

Tilapia will consume mosquito fern but are a warm water species that cannot survive in temperatures below 55° F. Therefore, tilapia usually cannot be stocked before mid-April or May and will die in November or December. Recommended stocking rates are 15 to 20 pounds of mixed sex adult Mozambique tilapia (Oreochromis mossambicus) per surface area. Tilapias are often not effective for vegetation control if the pond has a robust bass population due to intense predation.


The active ingredients that have been successful in treating salvinia include diquat (G), fluridone (E), E = excellent, G = good.

Azolla (mosquito fern, duckweed fern, fairy moss, water fern, azolla caroliniana) is a genus of seven species of aquatic ferns, the only genus in the family Azollaceae. They are extremely reduced in form and specialized, looking nothing like conventional ferns but more resembling duckweed or some mosses.

Azolla has been used, for at least one thousand years, in rice paddies as a companion plant, because of its ability to both fix nitrogen, and block out light to prevent any competition from other plants, aside from the rice, which is planted when tall enough to poke out of the water through the azolla layer.

As an additional benefit to its role as a paddy biofertilizer have been used to control mosquito larvae in rice fields. The plant grows in a thick mat on the surface of the water, reducing the rate at which oxygen dissolves into the water, effectively choking the larvae.

Resources: Wikipedia

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Products to Control Azolla

Planktonic Algae

WhiteCap is a fluridone compound and has been effective on coontail. It 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.


Redwing is a liquid diquat formulation that has been effective on coontail. It is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

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