Frequently Asked Questions


Swimming Pools

Q. What authority do you have regarding neglected swimming pools?

A. We appreciate attention to maintaining pools in a manner that does not produce mosquitoes. If the pool or other sources produce mosquitoes, we have the authority to initiate legal procedures pursuant to Civil Code Section 2929.3 and Health and Safety Code Sections 2020 and 204(m). A copy of our Districts’ resolution is available for perusal.

West Nile Virus

Q. Do we expect more human cases this year?

A. We remain very confident that our mosquito control program will have a significant impact on keeping human cases to a minimum. No one can predict the number or severity of cases.

Mosquito Fogging Notification

Q. How do you notify people and why can’t you do it sooner?

A. We have a very comprehensive response plan that relies on real-time data about mosquito populations, virus transmission and weather conditions. Once we determine that there is a risk to the public, we act immediately, sometimes within hours of our decision to fog or spray, before the mosquitoes fly away and the conditions to control them change. People wishing to be notified about adult mosquito fogging or spraying have several options. They may visit the District’s web site and opt to receive notifications automatically by email, they can view information on the District web site, or they may phone the District for a recorded message at (925) 685-9301. We also work closely with the media, though, they are not always able to publish or announce the information in time of advanced notifications.


Q. Will spraying pesticides hurt my vegetables, fish, or my car?

A. No. To our knowledge, there is no evidence to suggest harm to vegetables or cars. The materials we use pose little risk to people or the environment and are not applied directly to crops, weeds, or water. These materials have been used extensively and successfully throughout the country for decades.

Q. Do the products you use hurt bees and butterflies?

A. Our application methods minimize impacts to insects like bees and butterflies because treatments are made during times of the day when they are not actively foraging and are protected by their hives or resting areas. Also, the dosages/droplet sizes are designed specifically for tiny insects like mosquitoes; much higher dosages would be required to cause significant harm to bees or butterflies which have many times the body mass of a mosquito. We do not apply products to blooming crops or weeds. Finally, mosquito control districts have used EPA registered public health pesticides for decades with insignificant evidence of harm to these insects.

Q. Is spraying your last resort?

A. Fogging or spraying is the only known way to control adult mosquitoes. The majority of our mosquito control is done when the mosquitoes are in the water in their larval form. We are spraying or fogging for adult mosquitoes because adult mosquitoes in the area are infected with West Nile virus and are capable of infecting people.

Q. I heard there are special precautions people need to take, such as rinsing off children’s toys, turning off air conditioners, staying indoors, etc. What do people need to do?

A. There is nothing that people need to do because we are spraying or fogging for mosquitoes. The products we use are registered with the Environmental Protection Agency for controlling adult mosquitoes and protecting public health.

Q. What if people are sensitive to chemicals?

A. Those individuals should consult their doctor regarding their specific concerns. A list or our spray materials can be found here. All of our products are registered with the Environmental Protection Agency and applied by our trained and certified technicians.

Q. Where can I get additional information regarding specific insecticides?

A. Questions concerning specific insecticides can be directed to the U.S. Environmental Protection Agency, as this agency has responsibility for registration of insecticides. Many issues are addressed on the EPA’s Mosquito Control web site.

Q. Why are some mosquito control agencies aerial spraying and some are not? If some are not spraying, is it because it DOES cause problems?

A. As part of our Integrated Vector Management (IVM) program, every effort is placed on preventing mosquito production in the first place by eliminating standing water, using mosquitofish, or larvaciding. When and if aerial spraying becomes necessary to protect public health, we will use materials registered with the Environmental Protection Agency exactly for this purpose. We will make every effort to inform residents should spraying or fogging be necessary. All mosquito control agencies share the same goal; to protect public health; however, each agency operates autonomously and has the ability to protect public health in a manner they deem appropriate. Each situation is unique and must be evaluated exclusively to determine the best course of action given the terrain, type of mosquito, weather, etc.

Q. Many Districts rely heavily on adulticiding as their primary form of control. Does your agency?

A. We do not. We practice Integrated Vector Management relying on biorational larvacides, with adulticides reserved for situations where other methods would be ineffective to protect public health.

More questions and answers regarding mosquito spraying can be found by clicking here.

Seasonal Help

Q. Do you expect more West Nile virus cases this year or do you expect us to see a rise in the overall mosquito population? Will your District be hiring any seasonal workers this year to help fight mosquitoes?

A. We are not able to predict a higher virus risk since there are numerous factors that affect the risk. For example, weather, abundance of mosquitoes, abundance of birds carrying the virus, number of abandoned swimming pools and other water sources, and much, much more. We focus on areas of the county that our surveillance elements indicate as areas of potentially higher risk. In past years, we have used seasonal help to assist in surveillance and control of mosquitoes, but with shrinking budgets, we often utilize employees from our vertebrate programs to supplement the seasonal need. We assess our needs on a yearly basis. Our District is financially sound and our reserves have enabled us thus far to avoid layoffs of regular, full time employees; however, future revenues remain unforeseen. Redistribution our employees’ responsibilities is necessary at times. We have an excellent award-winning Public Affairs department that continues to utilize engaging communication methods to work with our constituents. Residents and business owners play an enormous role in helping to reduce risk of vector-borne diseases in the county, for it is often from urban, man-made sources that we experience large numbers of mosquitoes. We will continue to promote best management practices and keep the public informed about our efforts to minimize vector-borne disease risk to the public.

Dead Birds

Q. How come you don’t pick up and test ALL dead birds reported to you?

A. We appreciate all dead bird reports. West Nile virus is a serious disease and reporting dead birds gives us crucial information for our surveillance and control efforts. Not all birds can be picked up and tested, but just the report itself provides crucial information for our surveillance and control efforts.

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