The Merced County Mosquito Abatement District uses a science-based, targeted approach to control mosquitoes and reduce the risk of mosquito-borne diseases. Chemical treatments are one part of our integrated vector management program and are only used when necessary to protect public health.

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How We Monitor and Respond

Our technicians conduct routine inspections throughout the county to locate mosquito sources, including:

• Residential backyards
• Agricultural areas and farmland
• Curb and gutter systems
• Dairy lagoons and other water sources

Whenever possible, mosquito sources are eliminated. If a source cannot be removed, or is known to produce mosquitoes regularly, we apply appropriate treatments.

 

 

Treatment decisions are based on:

• Source type and size
• Mosquito numbers observed during inspection
• Mosquito trap counts
• Presence of mosquito-borne disease
• Number of service requests in an area

 

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Larval Mosquito Control (Larviciding)

 

The most effective way to control mosquitoes is before they become flying adults.

We apply larvicides to standing water and areas prone to flooding, where mosquitoes lay eggs. These treatments:

• Target mosquito larvae in water
• Are applied as liquids, granules, or briquettes
• Prevent mosquitoes from developing into biting adults

Larvicides are used in areas like pastures, storm drains, ponds, neglected pools, and other standing water that cannot be removed.

 

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Adult Mosquito Control (Adulticiding)

When adult mosquito populations are high or disease risk increases, we use adulticides to quickly reduce the number of biting mosquitoes.

Truck-Mounted Fogging Treatments

Truck-mounted foggers release an ultra low volume fine mist (fog) of insecticide into the air to target flying mosquitoes.

Benefits:

• Quickly reduces mosquito populations
• Helps lower the risk of disease transmission
• Targets areas with high mosquito activity

 

 

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Residential Treatments

 

 

In certain situations, we provide backpack (residual) treatments at individual properties.

• Applied to shaded areas where mosquitoes rest
• Targets vegetation, under eaves, and other cool, moist areas
• Provides control for up to one month

 

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Aerial Treatments

 

When mosquito-borne disease activity is widespread, aerial treatments may be used.

• Treats large areas quickly and efficiently
• Uses very low volumes of larvicides or adulticides
• Conducted at times that maximize effectiveness and minimize impacts to pollinators

This method is used only when necessary to protect public health.

 

 

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What to Expect During Mosquito Treatments

If treatments are scheduled in your area, here’s what you can expect:

Before Treatment

• The District will notify residents through:
  • Website updates
  • Social media: Facebook, Instagram, Nextdoor
  • In some cases: news releases

During Treatment

• You may see a District truck driving slowly through your neighborhood
• A light fog or mist may be visible in the air
• Treatments typically occur from early evening to early morning hours

After Treatment

• Mosquito populations typically decrease over the next few days
• You do not need to leave the area during or after spraying
• You may choose to:
  • Stay indoors
  • Close windows and doors
  • Bring pets inside

These steps are optional and not required.

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Are These Treatments Safe?

Yes. All products used by the District are:

• Registered with the U.S. Environmental Protection Agency (EPA), the California Environmental Protection Agency (CalEPA), and the California Department of Pesticide Regulation (CDPR)
• Applied by trained and licensed professionals
• Used according to strict label instructions

When applied properly, mosquito control treatments do not harm people, pets, or the environment.

If you experience any health concerns after spraying, contact your healthcare provider.

To learn more about the products we use for our mosquito control efforts, please visit our "Public Health Pesticide Information" page. 

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Ongoing Monitoring

Mosquito control is an ongoing effort. After treatments, we continue to:

• Monitor mosquito populations
• Conduct follow-up inspections
• Retreat areas as needed

Because mosquitoes reproduce quickly, treatments reduce populations temporarily and are applied as conditions change.

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Help Prevent Mosquitoes

You can help reduce mosquitoes around your home by eliminating standing water wherever possible.