Issue: July 24, 2004

Automatic mosquito control system


Concern about the West Nile virus has me afraid to go out into my garden this year. A friend told me about a system he uses in Louisiana that automatically sprays mist around his yard. Will that work here?


I was unaware of the automatic spray system, so I contacted Bonnie Rabe, Bureau Chief for Pesticide Management at the New Mexico Department of Agriculture. She stated concerns regarding the fact that it violated Integrated Pest Management (IPM) principles, safety, and it is often installed and maintained by people who do not understand how to safely use pesticides.

The automatic spray system violates IPM principles by spraying poisons into the environment even when there are no mosquitoes present. The poison may have negative effects on beneficial insects, pets, and residents. This is especially true if the wrong pesticides are placed into the system. Some people (residents or visitors to the home) may be allergic to even the proper insecticide, especially after prolonged exposure. By continuously applying pesticides into the environment without proper rotation of pesticide classes, insect resistance to insecticides will develop as it seems happened in Louisiana. If resistance to insecticides develops, mosquitoes that transmit West Nile virus and many other diseases may not be controlled and even worse outbreaks of disease can develop.

Another major concern is that the systems are installed and maintained by people not licensed in pesticide management. This results in systems that increase exposure of residents, visitors, neighbors, and pets to the pesticides. Large quantities of insecticides are stored in containers that may not be secured to prevent overturning by pets and children. A spill of large quantities (10 to 20 gallons of prepared insecticide) can result in a "point source" contamination and may result in groundwater contamination.

Finally, Bonnie suggested use of insect repellants when outdoors. This is especially important during the time when mosquitoes are active in early morning and in the evening. Generally, these are the times we are most comfortable outdoors, so the repellants are important. She stated that those insect repellants containing DEET are the only ones known to definitely provide protection and are the repellants recommended by the Centers for Disease Control. In recent years there have been concerns expressed about DEET, but you must decide which is the greater risk, West Nile virus (or Equine Encephalitis) or the DEET itself. There are other products that state that they repel insects, but they are products that have not provided efficacy data to the pesticide management agencies. Even citronella, which has proven to be somewhat effective as an "area repellent," has no data to prove that it is effective as a "personally applied repellant."

Bonnie states that the best approach is to contact county or city vector control agencies to see what they are doing. You don't want to add to the environment insecticides above and beyond what they are already using. If you have a mosquito problem, these agencies can help you. Bonnie also advises removal of all sources of mosquito infestation by draining any standing water on your property. It is a good idea to drain and rinse pet water dishes at least weekly, remove any old tires that may collect water, or any other containers that collect water from irrigation or monsoon rains. Rey Torres, Taos County Extension Agent, has written an excellent, concise publication discussing West Nile virus and efforts that can be taken to protect you and your family.

It is important to be aware of potential hazards but not over-react. Be cautious, use repellants, but avoid the mist systems that provide general sprays to your home environment even when you do not need the insecticide to be applied. Above all, continue to enjoy your garden but with awareness of the potential hazards.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


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