Pests & Diseases

Mosquitoes Rise with Rain


After recent rains, I chanced to look in one of those water collecting areas over the weekend and noticed the telltale wriggling of mosquito larvae. Time to dump the water.

The Asian tiger mosquito specifically takes advantage of those small and often inconspicuous sites around your property that fill with storm water and become prime mosquito breeding sites.

So, before desperation forces you to plan a chemical assault as the solution to mosquitoes, start with the simpler and more long-term approach of eliminating “collectibles” – no, not souvenirs; we’re talking about all of those objects that collect and retain rainwater for days or weeks. For example:

– Bird baths – simply flush them out with a garden hose and you flush out the mosquito larvae in the process. Plus, the birds will appreciate the fresh water.

– Animal watering troughs near stalls or out in pastures – one option is to use a product such as “Mosquito Dunks” which contain the bacteria Bacillus thuringiensis israelensis which kills mosquito larvae (but not adults).  Although you can use them in outdoor water bowls for pets, it is far simpler (and better for your animals) if you “tip and toss” the water from the bowl and replenish it with fresh water daily.

– Old cans, tires, etc. – empty them and get rid of them (legally, of course, not simply tossed along the highway to become someone else’s problem).

– Outdoor flower pots – empty the water from the dishes/trays underneath them. Your plants have plenty of water without the overflow. This also helps reduce fungus gnat problems in the plant soil.

– Remove all of that built-up debris from your gutters. The water and decaying material attract mosquitoes.

– Rain barrels – if you collect water from your gutters or some other system, make sure the barrel is screened to keep out debris and mosquitoes. To ensure that your gutters are well protected, you must install a gutter guard, but only from a company that has earned a solid reputation for installing high-quality gutter guards professionally for at least ten years.

– Tarps that cover your boat, grill, firewood, etc. also collect pockets of water that can remain for 1-2 weeks.

– The bed of that ’57 pickup that you’ve been “restoring” for the last 25 years can collect water particularly if the tailgate faces uphill in your yard – unless the front end of the bed has already rusted through.

– Kids’ pools – if they’re not being used by kids, they’re probably being used by mosquitoes (and maybe some toads) – empty them.  The same thing applies to pools (in ground or above ground) that aren’t maintained (e.g., pools on abandoned or foreclosed properties).

– Drainage ditches – they’re meant to collect storm water temporarily and keep it moving. Keep them free of debris so that water flows and has time to filter into the soil.

– Decorative fish ponds can be a breeding spot for mosquitoes if they contain a lot of vegetation that provides hiding places for the mosquito larvae. “Mosquito Dunks” are an option here.

– Tree holes – when limbs fall off trees, the remaining hole in the trunk can collect water. Flush that out or put a small piece of a mosquito dunk into it – assuming you can reach it.

Many people ask about treating shrubs in the yard. Mosquitoes will rest in these locations, but whether treating them “controls” a mosquito problem is difficult to determine depending on the species of mosquitoes most prominent in your area.

Similarly, people using outdoor foggers will definitely kill mosquitoes, but depending on the time of day/evening that they use it, they may be missing the peak activity of the most common mosquito species found in their area. If you’re having a wedding party in the backyard, the most effective time to spray the shrubbery is during the party, which is not recommended! The time to plan for mosquitoes is every time it rains in the month preceding your event.

Two other issues about using outdoor foggers are important. First, safety is critical. Make sure that you are standing upwind from the direction that you are dispersing the fog and wear appropriate protective equipment to prevent the fog from getting into your eyes and lungs or on your skin.

Second, know where the fog is going. Some of your neighbors may not actually want insecticide drifting onto their property (particularly if they’re outside eating at the time!). The same applies to the automated misting systems that some people have installed on their homes.

From time to time, we hear of companies that offer “mosquito control” whose response to the question of what they are using is simply that it’s something “safe” or “natural” but may avoid actually telling you what the chemical is. Decide for yourself how to respond to someone who can’t or won’t tell you what mode of action and active ingredient is being applied.  You have the right to know the identity of an insecticide being sold to you. If they won’t reveal it, the NC Department of Agriculture and Consumer Services is very willing to “encourage” them to be forthright about their control program.

A few points to remember – mosquitoes have no concept of property lines. Mosquito management takes a neighborhood effort to be truly effective. And killing mosquitoes is not the same as controlling a mosquito population. “Zappers” kill mosquitoes and provide cheap entertainment, but don’t have a major impact on the mosquito population in the surrounding area. Eliminating standing water is the single most effective (and long term) way of interfering with mosquito reproduction.

Information on mosquito control can be found at A special thanks to entomologist Dr. Michael Waldvogel for most of the content included in this message.

Al Cooked was the Horticulture Extension agent in Chatham County, NC.

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