Wet Weather Brings Mosquitos!

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Asian tiger mosquito

The Asian tiger mosquito can spread both West Nile Virus in humans and heartworms in cats and dogs.

Many areas of the state saw significant rainfall  last week and that also means they will see a rise in mosquito activity particularly by the Asian tiger mosquito which takes advantage of those small and often inconspicuous sites around your property that fill with storm water and become prime mosquito breeding sites. Before you start planning a chemical assault on your yard as the solution to mosquito problems, you need to start with the simpler and more long-term approach of eliminating “collectibles”. I don’t mean souvenirs; we’re talking about all of those objects that collect and retain rainwater for days-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. For horse owners with water troughs near stalls or out in pastures, one option is to use a product such as “Mosquito Dunks”, which contain “Bacillus thuringiensis israelensis”, a naturally occurring bacteria that kills the mosquito larvae (not the 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, 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
  • 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 Ford pickup that you’ve been “restoring” for the last 25 years can collect water particularly if the tailgate faces uphill in your yard.
  • Kids’ pools – if they’re not being used by kids, they’re probably being used by the 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. Keep them free of debris so that water flows and has time to filter into the soil.
  • Decorative fish ponds can be a source of 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.

Many people ask about treating shrubs in their 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. 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 chemicals 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 get reports 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 they won’t actually tell you what the chemical is. Personally, I would steer clear of a company that isn’t willing to tell you what they are spraying (or propose to spray) on *your* property. You have the right to know the identity of the product and 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.

One other point to remember – mosquitoes have no concept of property lines. Mosquito management takes a neighborhood effort to be truly effective. We have information on mosquito control on the web at http://insects.ncsu.edu/Urban/mosquito.htm.


This article written by:

Michael Waldvogel, PhD
Extension Assoc. Professor & Specialist, Structural & Industrial Pests
North Carolina State University