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Yes, Dawn dish soap mixed with water can kill mosquitoes that come into direct contact with it. It can also kill mosquito larvae in standing water because detergent lowers the water’s surface tension and interferes with the larvae’s ability to stay at the surface and breathe.
However, Dawn is not a good general mosquito-control treatment for rain barrels, cisterns, ponds, or other stored water. It is a dish detergent, not a registered mosquito larvicide. Its effects can vary, and adding detergent can make stored rainwater unsuitable for some uses.
How Soapy Water Affects Mosquitoes
Dish detergent changes an important property of water called surface tension.
Surface tension is what makes the top of water act a little like a thin skin. Mosquito larvae live underwater but must reach the surface to breathe air. Many larvae use a small breathing tube, called a siphon, while hanging from the surface.
Dish detergent lowers the surface tension. Larvae may no longer be able to stay at the surface normally, which can cause them to drown.
Soapy water can also kill some adult insects when they become coated or submerged. But this requires direct contact.
Simply putting a bowl or bucket of soapy water outside does not attract enough adult mosquitoes to provide useful mosquito control. Iowa State University Extension specifically lists pans of dish detergent and water among methods that do not have a meaningful effect on mosquito populations.
Does Dawn Kill Mosquito Larvae in a Rain Barrel?
It may kill mosquito larvae, but adding Dawn to a rain barrel is not the preferred solution.
Dawn and similar dishwashing liquids are detergents. Their formulas are made for cleaning dishes, not treating stored water or controlling mosquitoes. The strength and ingredients can also differ between products.
Adding enough detergent to affect mosquito larvae may leave detergent in water that you planned to use later. That matters especially if the barrel supplies:
- Vegetable gardens
- Sensitive plants
- Ponds or other areas with aquatic life
- Animal watering systems
- Household water systems
- Water that could ever be considered for drinking
Dish detergents can also injure plants at some concentrations. Iowa State University Extension warns that household dish detergent is not a substitute for insecticidal soap and can cause plant damage.
For a rain barrel, it is usually better to prevent mosquitoes from reaching the water in the first place.
Better Ways to Keep Mosquitoes Out of Rainwater
The CDC recommends tightly covering water-storage containers such as rain barrels and cisterns. Where a solid cover is not possible, openings should have mesh with holes smaller than an adult mosquito.
Check the entire system, not just the top of the barrel.
Screen the inlet
Put fine mosquito-resistant mesh anywhere mosquitoes could enter with the incoming water.
Keep the screen clean. Leaves and roof debris can block it and cause the barrel to overflow in the wrong place.
Protect the overflow
An open overflow pipe can become a mosquito entrance.
Use an appropriate screen or closed fitting while making sure the overflow can still carry the expected water flow. Do not use mesh so restrictive that debris easily blocks the overflow.
Check hoses and fittings
Mosquitoes need only a small opening to reach standing water.
Look around:
- Downspout connections
- Inspection lids
- Overflow fittings
- Vent openings
- Loose covers
- Hose connections
Repair damaged screens and replace lids that no longer close properly.
Remove nearby standing water
The rain barrel may not be the source of the mosquitoes.
Once a week, the CDC recommends emptying and scrubbing, covering, turning over, or removing outdoor objects that hold water. Mosquitoes can breed in buckets, plant saucers, toys, gutters, and many other small containers.
What If Mosquito Larvae Are Already in the Barrel?
Consider mosquito controls for rainwater tanks to verify tank material choices for the intended end use.
If the rainwater can be emptied safely, draining and cleaning the barrel removes the larvae along with accumulated dirt and organic material.
Then find the opening mosquitoes used to get inside before refilling the barrel.
For standing water that cannot be emptied or covered, mosquito larvicides may be an option. The CDC specifically lists rain barrels among places where larvicides can be used. However, its homeowner guidance says to use larvicides for standing water that will not be used for drinking and to follow the product label.
One common larvicide is Bti, short for Bacillus thuringiensis israelensis. It is a bacterium used to control developing mosquito larvae. EPA-registered Bti products are available for mosquito control, including use around containers where water collects.
Use only a product whose label allows your specific situation, and follow the label directions. Do not assume that because a treatment is suitable for one rain barrel, it is suitable for water intended for drinking, livestock, fish, or another sensitive use.
What About Water That May Be Used for Drinking?
Do not add Dawn to stored rainwater intended for drinking.
Roof runoff can already contain germs, bird and animal waste, dust, metals, roofing residues, and other contaminants. Adding detergent creates another contaminant that a drinking-water treatment system would need to address.
Collected rainwater is not automatically potable. Potable means suitable for drinking.
If rainwater is intended for drinking, mosquito prevention should be built into the collection system with sealed storage, screened openings, good roof-water management, appropriate treatment, maintenance, and current water testing. The CDC also recommends keeping rainwater systems properly maintained and preventing collected rainwater from contaminating safe piped drinking water.
Dawn Versus a Mosquito Larvicide
Dawn can sometimes kill larvae, but that does not make it the best treatment.
A mosquito larvicide is made and labeled specifically to control mosquito larvae. A household dish detergent is made to clean dishes.
That difference matters in stored rainwater because you need to consider more than whether the larvae die. You also need to know what will happen to the water afterward.
For most rainwater systems, the better order is:
- Block mosquitoes with tight lids and fine screens.
- Fix openings around inlets, vents, and overflows.
- Remove larvae and clean the container when practical.
- For non-drinking water that cannot be drained or covered, consider an appropriately labeled mosquito larvicide.
- Avoid adding household detergents as a routine treatment.
This approach controls the mosquito problem without unnecessarily adding cleaning chemicals to stored rainwater.
Frequently Asked Questions
How much Dawn should I put in water to kill mosquitoes?
There is no standard Dawn dose recommended by the CDC or EPA for treating mosquito-infested rainwater. Dawn is a household detergent, not a mosquito larvicide. For rain barrels and other stored water, use physical mosquito barriers or an appropriately labeled larvicide instead.
Will a few drops of dish soap kill mosquito larvae?
Dish soap can lower surface tension enough to interfere with mosquito larvae at the water surface, so larvae may die. The effect can vary with the detergent, water volume, and other conditions. It is not a reliable substitute for proper mosquito control.
Does soapy water kill adult mosquitoes?
It can kill adult mosquitoes that become coated or submerged in the solution. However, a container of soapy water does not attract enough mosquitoes to be an effective way to control the local mosquito population.
Can I put Dawn in my rain barrel?
It is better not to use Dawn as a routine rain-barrel mosquito treatment. It adds detergent to water you may want for plants or other uses. Keep the barrel tightly covered and screen all openings instead.
What can I put in a rain barrel to stop mosquito larvae?
Prevention with tight lids and mosquito-resistant screens is the first choice. For standing water that cannot be emptied or covered and will not be used for drinking, the CDC says appropriately labeled mosquito larvicides can be used. Always follow the product label.
Are mosquito dunks better than dish soap?
For suitable non-drinking-water applications, a properly labeled mosquito larvicide such as a Bti product is a more appropriate choice because it is specifically designed and registered for mosquito control. Check the label to make sure the product fits your water use.
How do I keep mosquitoes from breeding in a rain barrel without chemicals?
Keep the barrel tightly covered, put fine mesh over every opening mosquitoes could enter, screen or protect the overflow, repair damaged screens, and remove nearby standing water. Periodically inspect and clean the barrel as needed.
