- Author: Andrew Sutherland
Many gardeners have fountains, ponds, and other water features in 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 prevent mosquito infestations?
How do mosquitoes develop?
First, it is important to understand mosquito biology. Mosquitoes are small flies that lay their eggs in, on, or near stagnant water. The larvae, or wigglers that hatch from the eggs live in water and feed on organic debris until they transform into a motile pupa, or tumbler, and finally into the familiar adults. This process, from egg to adult, requires as little as one week when conditions are favorable. Emerging females must mate and ingest blood to produce new eggs.
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?
Tips for managing mosquitoes in water features
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. Add a fountain, waterfall, or other device that 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. For larger ponds, a pond skimmer will help keep mosquitoes and the algae that favors them under control. If you have a smaller pond, you can use pond skimmer nets. If fertilization is required, use pond spikes designed to prevent algae blooms.
In natural environments, bacteria, nematodes, other insects, crustaceans, and fish often keep numbers of mosquito larvae low. Protect 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 their 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.
Pesticides for mosquito larvae
Use larvicides specially designed for use against mosquitoes in water. Larvicides containing spores or metabolites of the bacterium Bacillus thuringiensis ssp. 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 and remain effective for about a month. As with all pesticides, use these only according to label directions.
For more information about mosquitoes, visit https://ipm.ucanr.edu/PMG/PESTNOTES/mosquitoes.html.
[Featured in the Summer 2024 edition of the Home and Garden Pest Newsletter]
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Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
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Help Desk Response: Thank you for contacting the UC Master Gardener Program of Contra Costa County. We are unable to locate any specific research which directly addresses your question about fountain height as a raccoon deterrence but have some general recommendations. We also know that raccoons are quite agile, strong, and industrious in the garden, especially where water features are present.
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It is appropriate for you to deter raccoons from using your fountain as the Center for Disease Control and Prevention (CDC) states that raccoons like to defecate in shallow water (and elsewhere as well) and their feces can contain eggs of the worm Baylisascaris Procyonis, which can infect humans and cause a neurological illness. The CDC recommends placing spikes at the bottom of the pool (e.g., nails in boards would work). Other possible deterrents are to install a fountain that has steep rather than sloping sides, dropping to a foot or more, and/or to cover the fountain with a heavy screen at night.
The University of California Integrated Pest Management Program (IPM) recommends a number of steps for managing raccoon pests which include how to detect their presence, habitat modification, and exclusion. The overall recommendation is to ensure that you and your neighbors are not attracting them by providing them food or nesting dens. If the suggestions above don't work, excluding them from pools (or fountains) can also be accomplished by installing commercially available devices with one or two low-lying electric wires, 6 and 12 inches from the ground, around the pond or fountain, and activated only at night via a timer.
For additional information on raccoons in the garden, please see the UC Pest Note below:.
http://ipm.ucanr.edu/PMG/PESTNOTES/pn74116.html
Thank you again for contacting us and please let us know if you have any additional questions.
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Help Desk of the UC Master Gardener Program of Contra Costa County (NP)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925)646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
/span>- Author: Janet Snyder
Sometimes I sit in my garden and enjoy listening to the quiet. I spend the better part of my day listening to kids, and I wouldn't have it any other way, but every now and then I just love to hear the quiet. However, lately I have been sitting out there and thinking it would be really nice to have some sort of fountain. I've had a birdbath for a number of years, and I keep it full of fresh water because so many birds stop by it every day. They love to take a short "dip" in the water and then fly off. I figure that the little sounds of water I hear when they are bathing would be that much nicer to hear coming from the sound of a small fountain, right?
Most of us have heard that the sound of water can be very soothing and even help lower our stress level. It can actually help cool you down to hear the sound of water on a hot day, and with the intense heat we are prone to in the summer, that could be a very good thing. The area around the fountain, having a higher level of humidity, is great for the plants in the garden. Also, the addition of any water feature in a landscape is beneficial to the birds and insects we want in our gardens. It gives them a place to rehydrate and cool off.
I think I have convinced myself that it's time for a fountain!
- Author: Bryon J. Noel
We have had some special guests at the office this past weekend. They have really enjoyed their time here. And it looks like they don't want to leave. These are wild Turkeys that freely roam the City of Davis.
The shot here is classic... The male in the background strutting his stuff and the female (?) standing on the fountain getting a drink of water.
![Image: Two Turkeys, one standing on a fountain getting a drink of water. A male turkey in the background strutting showing a full bloom of feathers. Image: Two Turkeys, one standing on a fountain getting a drink of water. A male turkey in the background strutting showing a full bloom of feathers.](http://ucanr.org/blogs/wat/blogfiles/6793.jpg)