How to Kill Mosquito Larvae in a Pond

Mosquitoes aren't just itchy annoyances. These flying pests can harbor several diseases, including dengue fever and the West Nile virus. Residential ponds and water gardens can become breeding grounds for mosquito larvae. Eradicate the larvae from your pond and you will not only restore its natural beauty but also break the mosquitoes' life cycle and help eliminate these biting pests from your yard.

Lotus flower
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A water garden can attract mosquitoes if not cared for properly.

Keep it Clean

Use a handheld net to skim floating leaves, sticks and other debris off the pond's surface. Trim back dead and dying vegetation along the pond's borders. Remove overgrown pond plants; for the healthiest pond conditions, plants shouldn't cover more than 40 percent of the water's surface.

Floating debris, such as fallen leaves, and thick aquatic vegetation growth create a haven for mosquito larvae. The larvae feed on excess organic matter, and floating debris and heavy plant coverage protect larvae from predators and shield them from hot sunlight and harsh weather. For example, without the protection of floating debris or plants, mosquito larvae can die when rainfall disturbs the pond's surface.

Agitate the Water's Surface

Very calm, standing water is crucial for adult mosquitoes to breed and for the resulting larvae to survive. Using a simple pond aerator that makes bubbles and moves the water's surface can be enough to deter adult mosquitoes and kill the waterborne larvae. An aerator doesn't only repel mosquitoes; it creates a trickling sound of moving water that can add a sense of tranquility to the landscape's ambiance.

Additionally, consider keeping shrubs and other plants away from the edges of the pond to help create water surface movement caused by wind.

Enlist the Help of Predators

Mosquito larvae are defenseless to a wide range of natural predators. They include birds, amphibians such as toads and frogs, fish and dragonflies. Attract predators to the pond, and they'll keep mosquitoes and larvae in check.

Attract dragonflies by adding flat, dry rocks to the pond's edges, providing them resting spots. Additionally, avoid using broad-spectrum pesticides in the surrounding landscape to prevent accidentally killing dragonflies and other beneficial insects.

True to their name, mosquito fish (Gambusia affinis) feed on adult and larvae mosquitoes and can keep a mosquito and larvae problem from recurring. Introducing a few mosquito fish will bring life and color to your pond while effectively controlling mosquitoes. Do not add mosquito fish, however, if your pond is connected to a natural waterway. About one mosquito fish provides mosquito control for every 20 square feet of pond surface area.

Apply a Natural Larvicide

If practicing proper pond cleanliness, creating water movement and introducing mosquito predators don't satisfactorily control the number of mosquito larvae, then turn to an all-natural larvicide. The Bacillus thuringiensis israelensis, or Bti, bacteria poisons mosquito larvae without killing fish or beneficial predatory insects. Bti is available in pond and garden stores as granules, pellets or slow-dissolving tablets that you simply toss into the pond.

Follow labeled guidelines because the bacteria concentration varies by product. For example, granules with a concentration of 2.86 percent Bti are typically used at a rate of 1 teaspoon for every 25 square feet of pond surface area. Slow-dissolving tablets with a concentration of 10.31 percent Bti per tablet are often used at a rate of one tablet per 100 square feet of surface area. An application of Bti works for approximately one month.