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How is the Marin/Sonoma Mosquito & Vector Control District funded?

The Marin/Sonoma Mosquito & Vector Control District is a California Independent Special District and is principally funded by a very small portion (equivalent to its share prior to 1978) of the ad valorem property taxes collected by the County Tax Collectors. The second-largest source of financial support comes from two benefit assessments, which are annual service charges assessed on all non-exempt land parcels in the service area. Each year an Engineer’s Report (available for download on this site) details the special benefits accruing to each land parcel and the Board of Trustees sets the amount of the benefit assessment following a public hearing, typically in late Spring.

Due to a cap imposed when the main benefit assessment covering the majority of the two counties was set up in 1996, the annual amount for a single family equivalent parcel is $12 and can never be increased. Areas of West Marin and Sonoma Counties that voted to annex to the District in 1994 pay approximately $23 per parcel, but do not contribute ad valorem revenue, so the amount paid per households in both assessment districts is very similar.

Although the District does not charge fees to home and business owners for its services, and most public entities are exempt from the paying the benefit assessments described above, the District bills approximately $200,000 per year to agencies to which it provides contract services e.g. California Department of Fish and Wildlife and certain Sanitary Districts. The smallest source of revenue is the interest that the District earns interest on reserve funds kept on deposit for purposes such as emergencies and replacement of capital items.


The laws governing Benefit Assessments do not provide for any exemptions such as the senior, disability, low income or veterans property tax exemptions. Benefit Assessments are fundamentally different from property taxes as they reflect the provision of a direct benefit to the property and its residents, as opposed to a general tax assessed according to the property’s value (ad valorem tax).

Why is mosquito control important?

Not only are mosquitoes a nuisance, they are also a public health threat. While most mosquito species in Marin and Sonoma counties are considered nuisance mosquitoes, their bites can cause severe allergic reactions in some people. High populations of mosquitoes can also have an impact on livestock, negatively affecting milk production in dairy cows.

More importantly, mosquitoes must be controlled because of the risk to human health. Mosquitoes have the capability of transmitting diseases such as West Nile virus, dog heartworm and western equine encephalomyelitis. The goal of the District's mosquito control program is not to eradicate all mosquitoes, but to successfully reduce nuisance mosquito populations and prevent mosquito-borne disease transmission.

How do you control mosquitoes?

Mosquito and vector control is based on scientifically planned management tactics and control strategies that reduce the abundance of target pests in a timely manner. This method is commonly referred to as “Integrated Vector Management” (IVM). This comprehensive program incorporates five basic methods: public information and education, mosquito and vector surveillance, source reduction, biological control and microbial and chemical control.

How does the District notify residents of adult mosquito control (fogging)?

The District has implemented an Adult Mosquito Control Notification Program as a courtesy to the residents of Marin and Sonoma counties. This program utilizes Everbridge Communication System to send out notifications to send out pre-recorded messages 48 hours in advance to homes within a 0.5 mile radius of the area scheduled for truck mounted adult mosquito control (fogging). Maps of the scheduled treatment area can be viewed by clicking on the View Fogging Maps link.

Telephone numbers that are listed in the white pages have been provided via the Everbridge Communication System. Residents that do not have landlines or are not listed in the white pages will need to register online through the Everbridge Communication System website. Click here to enroll. This will take you to the Community Enrollment Page where residents can input and manage their contact information and preferred method of message delivery (landline, cell phone, text message, or email). Residents can also choose to opt out of receiving notification messages on the Community Enrollment Page.

Please note: It is the responsibility of the individual to maintain their current contact information.

What does the District use to control adult mosquitoes?

Adult mosquito control (adulticiding) is the only known effective measure of reducing adult mosquito populations in a timely manner. All mosquito adulticiding activities follow reasonable guidelines to avoid affecting non-target species including bees. Timing applications to when mosquitoes are most active, avoiding sensitive habitat areas, working and coordinating with property owners and personnel of other agencies when required, and following label instructions all result in environmentally sound mosquito control practices. Adult mosquito control may be conducted when all other methods of control have been exhausted or when larval control measures are unsuccessful or not possible. Most importantly, it is used for the quick knockdown of adult mosquitoes to break the disease transmission cycle.

The most common materials used by the District for adult mosquito control are pyrethrins and etofenprox. Pyrethrins are a group of naturally occurring compounds with insecticidal properties that are extracted from chrysanthemum flowers. Etofenprox is a low-toxicity pyrethroid; a synthetic version of pyrethrins.

These materials are applied in an ultra-low volume (ULV) form, similar to a fog. The tiny (micron-sized) particles impinge on flying mosquitoes. These materials affect the nervous system of insects by causing multiple action potentials in the nerve cells and delaying the closing of the ion channel. The Environmental Protection Agency (EPA) has determined that these adulticides, when used at labeled rates for mosquito control, do not pose unreasonable harm to the environment or humans. Label rates for mosquito control are normally less than one ounce per acre. These adulticides are extremely photosensitive and break down within hours in the sunlight. All products used by MSMVCD are EPA registered public health pesticides labeled for mosquito control. Applications of these products are conducted by state certified mosquito and vector control technicians in accordance with label requirements and limitations.

For more information on materials registered for mosquito control, visit the Centers for Disease Control website. 

How will the materials you use to control adult mosquitoes affect the health of humans and other animals?

The Environmental Protection Agency (EPA) has determined that pyrethrin-formulated adulticides, when used at labeled rates for mosquito control, do not pose unreasonable harm to humans, animals or the environment. Label application rates for mosquito control are normally very low (less than one ounce per acre). Pyrethrins are extremely photosensitive and break down within hours in the sunlight. 

There is no need to house your pets or livestock when an adult mosquito control application is being conducted: however, any concerns regarding animal health should be directed to a veterinarian.

People with chemical sensitivities could experience eye and skin irritation or an allergic type reaction if exposed to a pyrethrin-formulated adulticide application, and may want to contact their personal physician with any concerns.

All products used by MSMVCD are EPA registered public health pesticides labeled for mosquito control. Applications of these products are conducted by state certified mosquito and vector control technicians in accordance with label requirements and limitations.

What is the best insect repellent to use against mosquitoes?

Repellents can protect you from annoying insect bites and mosquito-borne illnesses. The Centers for Disease Control(CDC) recommend the use of insect repellents containing active ingredients that have been registered by the Environmental Protection Agency (EPA). Registration of these types of products means that they have been tested and proven to be effective and safe for humans when applied according to the label directions.

The following insect repellent active ingredients are registered with the EPA and recommended by the CDC:

  • Picaridin
  • Oil of Lemon Eucalyptus or PMD (not for use on children 3 years and younger)
  • IR3535

Please visit the CDC's Insect Repellent Page for detailed information about any of these repellents. 

How effective are bats at controlling mosquito populations?

Many species of bats feed on mosquitoes, but using them as the sole means for mosquito control is unrealistic. In fact, studies show that mosquitoes typically comprise less than 1% of a bat’s diet. Bats are opportunistic feeders and have not shown to prefer any one particular insect over the other. Bats themselves pose a health threat because they have the ability to spread fatal diseases such as rabies and histoplasmosis to humans.

Information source: American Mosquito Control Association

The best way to control mosquitoes on your property is to remove unnecessary standing water, stock mosquitofish in appropriate water features, manage and maintain ponds, swimming pools, hot tubs, and rain barrels, and remove items that can accumulate rain water. If you are experiencing a mosquito problem please contact us for advice.

How can I protect myself from ticks and Lyme disease?

Before entering tick habitat, take the following precautions:

  • Consider applying repellent containing at least 20% DEET to exposed skin.
  • Consider treating clothes/personal outdoor equipment with an acaricide containing permethrin.
  • Wear light-colored clothing (this makes it easier to spot ticks).
  • Wear long pants, long sleeves, and long socks whenever possible (this makes it more difficult for the tick to get to your skin).

While in tick habitat:

  • Stay on trails (adult ticks are typically more abundant on the uphill sides of trails).
  • Avoid contact with nymph habitat (leaf litter, logs, tree trunks, etc.).
  • Periodically check for ticks on people and animals.

After exiting tick habitat:

  • Wash all clothes in hot water and dry on high heat.
  • Shower after coming indoors and carefully check for ticks.
  • Properly remove any attached ticks immediately (please see our tick brochure for proper removal technique).

Reduce tick abundance around the home:

  • Utilize landscaping techniques that limit cover for ticks near the home, such as removing leaf litter around homes and using gravel or woodchip barriers between lawns and wooded areas (see the Tick Management Handbook for detailed information).
  • If properly timed, application of acaricides (pesticides designed to kill ticks) can be effective in reducing tick populations near homes. Residents should contact a private pest control company if they are interested in this service.

What areas do you treat by helicopter?

Helicopter larvicide applications are a relatively infrequent activity, typically making up only a small portion of the District’s larvicide applications each year, with each application covering approximately 20 to 600 acres per operation. Applications areas vary year to year. 

When do helicopter treatments occur?

Helicopter larvicide applications are deemed necessary when large areas, difficult to access areas, and/or areas with dense and/or abundant aquatic vegetation are producing mosquito larvae at densities exceeding District treatment guidelines. Treatments may be cancelled or postponed on short notice due to unfavorable weather conditions.

What products do you apply by helicopter?

Materials typically used during helicopter larvicide applications include BS (Bacillus sphaericus), Bti (Bacillus thuringiensis israelensis), a naturally occurring bacteria, and methoprene an insect growth regulator. Due to the fact that the mosquito larvae may in varying stages of the developmental cycle the use of these materials enables effective control of the larvae

How will I be affected by helicopter treatments near my home?

During a helicopter larvicide application you may hear and or see a low flying  helicopter. There is no need to relocate during the treatment as only targeted bodies of water are being treated. Depending on the location of the application, recreational trails may be closed for a short time.  Informational signs are posted near the application site.

Why do you use a helicopter instead of other equipment?

Treating these areas by helicopter allows for the efficient and direct application of mosquito larvicides into large water bodies and/or water bodies with dense vegetation. Aerial application, when appropriate, can also be an option in especially sensitive habitats.