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Mosquito management for ponds, fountains and water gardens

Mosquito larvae must come to the surface to breathe air through abdominal siphons. Photo by Jack Kelly Clark.
Many gardeners are adding fountains, ponds, and other water features to their landscapes. Water gardens are beautiful and calming, but, if not managed properly, can add an unpleasant element to the landscape—mosquitoes. How can you help prevent mosquito infestations?

Mosquitoes can be managed using an integrated approach that relies mostly on prevention, using biological and chemical controls when necessary. The key strategy is to eliminate all potential breeding sites; even one ounce of standing water can support a population of larvae. What can be done, however, when an outdoor space contains a water element? Here are a few tips.

Water features in the landscape will invariably attract adult mosquitoes, but attempting to control them or prevent their egg laying is difficult. Larvae are easier to manage, since they are concentrated in known areas, don't yet bite, and can't fly away. Larvae prefer shallow water that is less than 24 inches deep, so install water features that are deeper than 2 feet. Ponds or features that provide a steep slope or have vertical walls that quickly drop off into deep water will also be less favorable to mosquitoes. Adding a fountain, waterfall, or other device increases water circulation and reduces the stagnation that allows mosquitoes to breed.

Remove excess vegetation and organic debris that provide mosquito larvae with food, shelter from the sun, and hiding places from predators.

In natural environments, bacteria, nematodes, other insects, crustaceans, and fish often keep numbers of mosquito larvae low. Conserve predators such as dragonflies and backswimmers, which may have colonized ponds, by avoiding broad-spectrum insecticides and consider introducing fish. County vector control services may provide free mosquito fish, voracious consumers of mosquito larvae and pupae. Never release mosquito fish into natural water bodies, since these fish aren't native to California and can disrupt ecosystems.

Although these measures will prevent problems in most cases, mosquito larvae may still develop in some ponds.

In gardens with lots of plants growing in still water, it may be impossible to keep mosquitoes from breeding. Regularly check water features for larvae, which periodically come to the surface to breathe through abdominal siphons Watch for the larvae's characteristic wriggling movement, or use fine dip nets to monitor for larvae. It is important to act quickly to kill mosquitoes when they are small, easiest to manage, and before they become adults and start biting.

Larvicides containing spores or metabolites of the bacterium Bacillus thuringiensis israelensis (Bti) (e.g., Mosquito Dunks, Mosquito Bits, Microbe-Lift, and other products) act as stomach poisons when ingested, killing larvae within a few days. Bti affects only fly larvae, so it won't harm predatory insects living in the pond or water feature. Another effective larvicide is the insect growth regulator (IGR) methoprene (e.g., Pre-strike Torpedos). IGRs interfere with larval molting and also take a few days to kill, but they have a broader spectrum of activity, affecting most juvenile insects and other arthropods that might be in the pond. Both Bti and methoprene are available as granules or pellets, remain effective for about a month, and as with all pesticides, should be used only according to label directions.

For more information about mosquitoes, visit http://www.ipm.ucdavis.edu/PMG/PESTNOTES/mosquitoes.html.

This article by Andrew Sutherland, UCCE advisor in the San Francisco Bay Area and UC Statewide IPM Program, was originally published in the June 2013 issue of the Retail Nursery and Garden Center IPM News. Read the entire article at http://www.ipm.ucdavis.edu/RETAIL/retail-newsletter.html 

Posted on Friday, July 12, 2013 at 3:41 PM
  • Author: Andrew Sutherland
Tags: Andrew Sutherland (4), gardens (8), Mosquitoes (28)

Comments:

1.
Great article, but I have a related question:  
We love the tadpoles that appear at the same time as the unwanted mosquito larva. Last year we tried the donuts to kill the mosquitos however they also killed the tadpoles. To your knowledge, what is the best way to kill the larva and keep the tadpoles?  
Thanks, Scott

Posted by Scott on March 23, 2014 at 10:02 AM

2.
Scott,  
The 'donuts' you reference were most likely 'mosquito dunks', containing an active ingredient derived from a naturally-occurring soil bacterium, Bacillus thuringiensis israelensis (Bti). The metabolites from these bacteria are toxic to insects once ingested; they should have no effect on vertebrates such as tadpoles. Perhaps something else happened to kill your tadpoles. Look carefully at the product label next time you try this to make sure Bti is the only active ingredient and that you apply the correct amount. You may also consider mosquitofish as predators, available from your county's Vector Control program. Best regards,  
Andrew Sutherland

Posted by Andrew Mason Sutherland on April 3, 2014 at 10:38 AM

3.
Hi...This is a very informative article...I would just like to ask about the breathing capabilities of the mosquito larvae..How many minutes can they breathe below the water surface before they suffocate?

Posted by Ted on September 15, 2014 at 5:20 PM

4.
In an entirely balanced pond there is not any have to be compelled to feed the fish as they’ll eat two-winged insect’s larvae, water fleas, worms, plants. Shield pond with EPDM Pond Liners and leave to be troubled concerning damages and issues of pond.

Posted by joan Keeley on June 9, 2015 at 3:05 AM

5.
Mosquito is a threat to us in Africa, especially during the raining season. It is a disturbing issue here Nigeria. I wish scientist can improve on how to kill mosquito rather than making weapon for killing fellow men. We need to destroy this insect.

Posted by abdul on July 5, 2015 at 4:38 AM

6.
i have a small bubble fountain about 18" deep with recirculating water. We don't let it run continually. We now have a lot of Mosquitos. What can we pour in the water to kill in larvae and the Mosquitos flying around it?

Posted by Dillie on October 5, 2015 at 4:37 PM

7.
You can use Bacillus thuringiensis (Bt) products such as Mosquito Dunks, Plunks, or Bits, which contain a bacterial agent that kills mosquito larvae but doesn’t affect people, other animals or plants. For more information about mosquitoes, visit http://www.ipm.ucdavis.edu/PMG/PESTNOTES/mosquitoes.html

Reply by Pamela Kan-Rice on October 5, 2015 at 4:49 PM

8.
I hear just plain cooking oil keeps mosquito from leaving water. oil gets on the wings they can't fly and they die. but I wonder how this would affect fish,i'm thinking not good. but in a still pond i'll bet it will. anything to add,anybody?

Posted by carlene on October 27, 2015 at 7:59 PM

9.
I have been raising mangroves in my home for a while now, and they are getting too big to keep inside on the counter so I wanted to put them outside. However, I was concerned about their bowl becoming a place for mosquitos to breed. What can I put in the water that will keep that from happening but still not harm the mangroves?

Posted by Cheri E on May 14, 2016 at 6:18 AM

10.
Let me share with you one of my finding, which surprised me a lot when one of our student applied along with other plant based extracts from controlling mosquitoes larvae.  
It is an organic compounds and not toxic for fish.It kills mosquito larvae within one hour with 0.125 ppm concentration.In fact its a great finding and I want to go commercial on it.  
Dr Tariq Pakistan.

Posted by tariq nawaz khattak on May 14, 2016 at 9:36 AM

11.
We a inherited a small artificial pond, about ten feet long, two feet wide and two feet deep. Two years ago we placed ordinary "feeder fish" goldfish at 22 cents each, about an inch long. We have no fountain, no nothing, the fish are now over 6 inches long, had babies last year, and no more mosquitoes! We do feed them from april to october (we live on the west coast of Canada). Just be very sure there is no chance your pond could flood releasing fish into the natural waterways - this is would be extremely detrimental to the ecology of local waterways.

Posted by LORINNE on May 17, 2016 at 12:06 PM

12.
Virginia Beach has started its summertime effort to combat mosquito populations throughout the city and this year they are also keeping a close eye on the Zika virus. To avoid mosquito bites, get mosquito nets

Posted by Sophie on May 19, 2016 at 7:46 AM

13.
The old way to remove mosquitoes is to spray or pour a small amount of kerosene into the water. Obviously not where there is fish. This stops the larvae from breathing and the all die within hours. The kero seems to break down quite quickly and disappear. Cooking oil does not disperse over the water in the same way. You will see multicoloured reflections all over the treated areas.

Posted by Ali on May 31, 2016 at 4:25 PM

14.
Can Mosquito dunks etc. be run through a pump as in a water feature? Any other suggestions? I have birds that often come to bathe and splash in the waterfall and don't want to harm them in any way. Thanks

Posted by Jacqueline on June 7, 2016 at 12:43 PM

15.
I have saved rain in several large buckets. Will use in the next couple of weeks. Do I need to add something to prevent mosquito larva ?

Posted by SUS AN on July 6, 2016 at 10:10 AM

16.
A thesis written by Elizabeth Kathleen McCraven (University of New Orleans) Electro-Disinfection of Ballast Water, can be found on the web, it states that it is known that mosquito larvae is in ballast water. Her statements on mosquitos and ballast water are written in plain talk that speaks volumes about the way the ballast water is being looked for disease transmissions. Mosquitos feed on algae. New unexplained algae is showing up throughout the Great Lakes. Recent studies have shown large amounts of bacteria ,virus's and algae coming into the Great Lakes after an ocean flush.  
Without federal ballast water protection for ships exclusively using all the different Great Lakes, each with their distinctively different echo systems and problems. What new disease's such as Zika will the mosquitos species in the Great Lakes prove to carry? Florida is rampant with algae mosquitos feed on algae.

Posted by Don mitchel on August 29, 2016 at 10:16 AM

17.
I have a small fountain with recirulating water. I always thought that if there is movement in the water then mosquito's  
could not survive..well, just found black mosquito larvae along with little red worms in there. I am hesitant to use the "dunk" because my next door neighbor has bee hives and I do not want to harm the bees. The dunk claims it is safe for animals, fish and birds but nothing about bees. I have yet to year from the company. Please advise if dunks are bee safe. Thank you.

Posted by Joyce Sue on August 30, 2016 at 9:02 PM

18.
i want infortation about the mosquito larva

Posted by Biswajit rana on September 1, 2016 at 1:01 AM

19.
To address comments and concerns above about Bti products ('mosquito dunks'). This microbial insecticide is selective: it only affects fly larvae. It is especially active against mosquitoes, fungus gnats, midges, and other primitive flies. It should not affect adult bees adversely. Once dissolved / suspended in the water, it will circulate freely in pumped systems. Mosquito management should be practiced any time water will be standing for more than five to seven days. Make sure to read product labels to ensure pesticide use is allowed in your state and at your 'site'.

Posted by Andrew Mason Sutherland on September 7, 2016 at 10:52 AM

20.
I read that coffee grounds were effective in destroying mosquito larvae. True?

Posted by Lola robuck josey on September 11, 2016 at 8:10 AM

21.
To Lola robuck josey,  
 
I have never heard of using coffee grounds to 'destroy' mosquito larvae. I believe the main effects of such an application would be to acidify and reduce clarity of the water. This sounds like a terrible idea.

Posted by Andrew Mason Sutherland on September 13, 2016 at 10:25 AM

22.
Adding to what Lorrine has already said. A few small fish are the answer and goldfish will add interest and colour

Posted by Philip on November 26, 2016 at 3:37 PM

23.
does putting 6 or 8...drops of olive oil into water barrel stop the creation,life of larvae, mosquito living..?  
Thank You

Posted by steven Charles on April 23, 2017 at 11:52 AM

24.
RE: question posed by steven Charles: Some insecticidal oils are used by professionals and government agencies in large water bodies to prevent mosquito larvae from breathing at the surface, thereby killing them. I don't think these oils are labeled for general use by the residential public, however. I suggest you contact your county's Mosquito and Vector Control agency to learn about approaches in your area (http://www.mvcac.org/). They often provide free mosquitofish for use in containers or ponds.

Posted by Andrew Sutherland on April 24, 2017 at 10:33 AM

25.
We have a cistern system that collects water into a deep well-like structure. This is the first year that we live here and I am concerned about mosquitoes. Will this be a breeding ground for larvae or do they not breed in deep water with steep sides as mentioned in your article? Could I keep goldfish in a structure like this? I am afraid of decomposing fish or using toxic products as we use the water to irrigate our garden. Is BTI considered organic?

Posted by Michelle on May 16, 2017 at 12:26 AM

26.
By Eng. Monica Bhardwaj  
31/07/2017  
what's the name of fish which used in water for killed mosquitoes????

Posted by Monica Bhardwaj on July 31, 2017 at 1:08 PM

27.
After trying almost all ideas i came up with a conclusion that the best way to kill mosquito larvae is to keep fish and periodically change of water. It is better to keep guppy fish or cichlid fish and make drain in your ponds or water garden. Change water time to time. Sunlight also helps to avoid mosquito growth. Do not put any kind of oil because it will do nothing but create a mess.

Posted by Salman on August 11, 2017 at 10:46 PM

28.
I live in cape Town South Africa. We are experiencing the worst drought ever and are restricted to 87 litres of water per person per day. I have sadly had to switch off my pool pump and am using the algae water to flush toilets and water plants so they don't die, which is why I cant add chlorine. Now I have a breeding pond for a huge amount of mosquitos. What can I add to ONLY kill the larvae and not other insects or birds. I am desperate as I need the water and don't want to empty the very large pool, which could also damage the pool lining if empty

Posted by Victoria Kretschmer on November 1, 2017 at 8:54 AM

29.
I used the Dunks in my circulating fountain. Unfortunately, the Dunks broke up into little pieces which clogged my pump.  
I would like a liquid option that kills the mosquito larvae but not any other wildlife.  
Would like a suggestion of another product.  
Thank you

Posted by Patti Allen on June 24, 2018 at 10:50 AM

30.
Mosquitoes, especially in the tropical countries can cause sickness like dengue, so one really has to be considerate about how clean their ponds are for the safety of others. This is a very informative article and I think the most important thing is just regular cleaning and additional help from larvicides.

Posted by https://midwestponds.com/pond-fountains/ on July 12, 2018 at 6:36 AM

31.
Live on a high bank (25 ft) above a small river that floods periodically and leaves a meander with water maybe 100 yards long and 30 yards wide. It eventually dries but breeds mosquitoes. Any oil that may be safe for other wildlife?? Offer human beings to? Or another idea??

Posted by Daniel Fischer on July 22, 2018 at 7:30 PM

32.
I want to use Mosquito Dunks for my rain barrel water. Will this contaminate the water making it unusable in the yard and garden

Posted by Barbara on March 15, 2019 at 6:16 PM

33.
That is interesting that the mosquito larvae prefer shallow water over deeper water. My parents have a small pond in their backyard, I will have to go check it out and make sure that it is over 24 inches deep, even on the edges. If this works, they will be so grateful, they have had such an issue lately.

Posted by Shaylee Packer on November 20, 2019 at 6:00 AM

34.
can water treated with soap, vinegar, oil or dunks to kill mosquitos be safely used to water my garden

Posted by k j on February 29, 2020 at 3:33 PM

35.
Hi,  
 
In this quarantine I decided to grow waterlillys. I used a bucket to see if the would actually grow, and to my surprise it did. It still very small and the bucket is not big either. These dunks seem to be to big for the space. How do I know how much to introduce to my bucket ?  
 
Thank you

Posted by Cynthia on April 25, 2020 at 3:53 PM

36.
could I add vinegar or epsom salt to a pond to keep mosquitoes out? If birds drink from the pond would that harm them?

Posted by wendy winter on May 5, 2020 at 12:59 PM

37.
I have a pool that is 6 foot round and 3 foot deep. Could I use lavender oil in the water to stop mosquitoes.

Posted by Sara l Hamilton on June 8, 2020 at 12:12 PM

38.
Our pool is seldom used and has a layer of oak leaves on the bottom which darkens the water. The local health department assumes the pool was stagnant and posed a mosquito threat and threatened legal action. My son immediately dumped 20 lbs of chlorine in the pool which killed all life including the frogs which ate the larva. Will that chlorine kill the Bacillus thuringiensis?

Posted by Arthur John Haecker, III, on July 8, 2020 at 12:03 PM

39.
To address recent (2020) questions above:  
Vinegar, soap, and epsom salts are not registered nor recognized as mosquito control products and should not be used for this purpose. Some oils are effective against mosquito larvae since they form a physical barrier at the surface that prevents larvae from "breathing". With this said, only specific oil products have been tested against mosquitoes and registered as pesticides by the EPA; other oils, especially household oils or plant-based essential oils, should not be used and may have deleterious effects on plants growing in ponds and water gardens. Mosquito Dunks (or Mosquito Bits for smaller water volumes, such as the bucket referenced by Cynthia above) are registered Bti bio-insecticides for residential homes and gardens. Water treated with Bti should not pose hazard to vertebrate animals (such as birds) or to plants. Most Bti products contain live bacterial spores that may be killed by disinfectants (such as the chlorine treatment mentioned by Arthur above).  
 
I'm so glad this article continues to be so popular! Keep the questions coming.

Posted by Andrew Mason Sutherland on July 9, 2020 at 11:48 AM

40.
Is the water that the mosquito dunks are in safe for humans? We have a 15 gallon fountain in our yard. I’ve always used the dunks to control mosquito larvae. But now our toddler keeps playing in the water and licking her hands. Do I need to be concerned or is it such a small amount I don’t need to worry too much? Where the fountain is located, it’s impossible to block off or keep her out of it

Posted by Dee levenson on July 26, 2020 at 1:56 PM

41.
Hi, I have a fountain that heavily drips water in a 1-foot diameter pattern into a 4-foot diameter pool. It runs full time, and the pool averages about 1-foot deep. I have a big mosquito problem and wondering if they're breeding in the water, or even perhaps in the moist soil around the fountain from water that "bounces" out. My understanding is that the water needs to be "stagnant" for mosquitoes to breed, but how stagnant? And I've now read some mosquitoes breed in moist soil instead of standing water? Thank you!

Posted by Leon on September 17, 2020 at 6:42 AM

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