The Buzz on Mosquito Misting Systems

One of the fastest growing segments of the pest control business throughout the South is the installation of backyard mosquito misting systems. Such systems have grown increasingly popular in the past few years due to concerns over West Nile virus and other mosquito borne diseases. Some see these systems as a way to take personal control over mosquito problems in communities that have cut-back or eliminated community spraying activities.

Mosquito misting systems consist of a series of high pressure tubes and nozzles installed by a around a home, backyard or pool area. Connected to a pesticide reservoir, pump and timer, these systems come on one or more times a day to produce a fine mist of insecticide that kills mosquitoes.

The working principle behind these systems is quite simple. The mister nozzles break the spray solution down into very fine particles (50 micron or less size) which remain suspended in the air for varying lengths of time. It is estimated that in still air a droplet of 50 micron diameter (about half the width of a human hair) requires about 3.5 minutes to fall three feet(1 meter). The idea is that flying mosquitoes present in the air at the same time as the insecticide particles will contact the droplets and die from contact with the insecticide. Depending on wind speed, the mist may persist in the air for 1 to 15 minutes, killing mosquitoes and other flying insects.

All mosquito misting systems work in a similar manner. For mister systems to work they must disperse an insecticide capable of killing a small insect. Don't be misled by distributors who claim that their system is "chemical free" or uses a product that is "safe" for beneficial insects. An insecticide is any chemical (synthetic or organic) used to kill or repel insects. Most active ingredients that are toxic to mosquitoes are also toxic to beneficial insects. If you would like to have a butterfly garden in your backyard, for example, a misting system may interfere with your success.

All ingredients in mister systems should be considered potentially hazardous to humans in sufficient doses. On the other hand, to date I am unaware of any human health incidents associated with use of any of the mister systems. Citrus oil, cedar oil, and citronella are among the other ingredients sometimes installed in, or recommended for, misting systems; however few field data have been collected on the effectiveness of these other insecticides.

As far as safety to humans is concerned, pyrethrum is considered low in toxicity to humans and other mammals, including dogs and cats. However, some people with asthma or respiratory conditions may find pyrethrum irritating. It is possible, therefore, that pyrethrins in the air could trigger an asthmatic reaction. As a reasonable precaution, children with asthma should be kept out of backyards for at least 15 minutes after misting systems have run.

Despite these concerns, many thousands of mosquito misting systems have been installed in recent years and as yet, few incidents of human illness have been reported. By all accounts, where installed and used properly, pyrethrin-based mister systems do reduce nuisance mosquito populations. It is yet to be seen how widespread mosquito misting systems will become.
While mister systems may provide some relief from summertime mosquito problems for some homeowners there remain a number of questions and concerns about their use and safety. They include:

• There is inadequate research on the effectiveness of many of the ingredients in mister systems. Specifically we know little about the most effective rates and most appropriate timing cycles for backyard mosquito populations.

• There is much confusion and lack of regulation on who installs and adjusts applicator systems. Many or most installations are conducted by persons without licensing and training in pesticide application. In some cases homeowners with no knowledge of pesticides or pesticide safety will service their own systems.

• So far there is little known about the impact of mister systems on beneficial insects and other organisms. Fish, for example, are relatively susceptible to pyrethrins; but no research exists on the safety of such systems to koi and other desirable backyard fish.

• We don't know the potential impact of mister systems on mosquito susceptibility to insecticides. Many mosquito control professionals are concerned that the widespread use of misting systems may hasten the development of insecticide resistance in wild mosquito populations. If this occurs it would reduce the effectiveness of community mosquito spraying operations.

• Mosquito misting systems do not follow best management practices for insect control. Best management practices (also referred to as integrated pest management--or IPM) call for insecticides to be used only when a pest is determined to be present at unacceptable levels. Mosquito misting systems apply insecticide according to a timer without regard to whether mosquitoes are present or not.

• Automated mister systems almost guarantee that pesticides will be over-applied for mosquito control. Even in systems that are set by installers to turn on at proper times (evening and early morning), it is inevitable that some home-users will set their systems to come on at inappropriate times (when away on vacation) and frequencies (every day rather than when mosquitoes are present). Consider automated irrigation systems in your town and see how many come on daily and during rainstorms.

• It is difficult to prevent drift of insecticide sprays from backyards into other sites. Some drift of sprays into neighboring yards is probably inevitable as long as systems come on regularly without regard to wind speed and direction. In one instance a gardener whose neighbor installed a system observed dead butterflies in her butterfly garden. To some extent, all mister systems have the potential for contaminating the yards and environments of others who may not choose to spray for mosquitoes.