Mosquito Fern (azolla)

Control Options

Cultivation Options

Description of This Plant

Control Options

Mechanical/Physical

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

Biological

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. In Texas, only triploid grass carp are legal and a permit from the Texas Parks and Wildlife Department is required before they can be purchased from a certified dealer.

Tilapia will consume mosquito fern but are a warm water species that cannot survive in temperatures below 55o 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. In Texas, stocking of Mozambique tilapia does not require a permit from the Texas Parks and Wildlife Department. Any other species of tilapia would require a permit. Check with out County Extension Agent in other states for legality of stocking tilapia.

Chemical

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

Reward is the registered diquat label for aquatic use and has been found effective on mosquito fern. It is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

Sonar and Avast are fluridone compounds, come in both liquid and granular formulations, and have been effective on mosquito fern. These are broad spectrum, systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.

One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.

One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist you with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.

Many aquatically registered herbicides have water use restrictions. For General Water Use Restrictions click here.

To see the labels for these products click on the name. Always read and follow all label directions. Check label for specific water use restrictions.

Cultivation Options

Mosquito fern 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.