Effective Friday March 20th, 2020 - Building access CLOSED to the Public except with a SCHEDULED APPOINTMENT  For details:




Adulticiding is the final component of Integrated Pest Management. Although every effort is taken to eliminate mosquito larvae before they become adults, various factors make it impossible to eliminate every mosquito. Therefore, adult mosquitoes emerge from breeding sites or migrate into Cass County in search of a meal or a mate. 

Mosquitoes in the adult stage can be controlled while resting or flying. Our decision to initiate an application to control adult mosquitoes is based on surveillance results, inspections by field aides, sweep counts, and nuisance mosquito calls.

There are two ways to control adult mosquitoes.

1. Barrier/Residual Sprays

Backpack sprayers are used to treat vegetation where adults rest during the day. The mist put out by a backpack is controlled and can be applied to areas where it will not harm humans or pets. Residual sprays are intended to make a chemical barrier or fence between mosquito harboring areas or breeding site and an inhabited area. The insecticides used for barrier treatments last much longer in the environment than those applied by fogging. Cass County makes these application in public spaces such as parks, ballfields, and densely wooded areas. For instructions on how to spray your own property click here.

2. Ultra Low Volume Sprays or "Fogging"

In the evening, mosquitoes come out of hiding, making them susceptible to control materials applied by truck mounted "foggers". These applications typically occur a few hours before and after twilight. This period is when adult mosquitoes are most abundantly feeding and active. The idea behind truck mounted and aerial spraying is to release the insecticide in as many very fine droplets as possible. Adult mosquitoes are killed when they come into contact with one of these droplets as they are flying. If mosquitoes are not present or are not flying at the time of the application it is useless.

For a full listing of Cass County Vector Control's Spraying Schedule, please click: Scheduled Adult Mosquito Control

For information, product labels, and MSDS for all adulticides used by Cass County click: Adult Control Products

For information about how you can control mosquitoes in your yard and immediately improve conditions click: Mosquito Spraying

There are several reasons that we may not spray during the scheduled time and date:

1. No Spray Zones - areas where people have requested no spraying due to health concerns or other reasons. 
2. Bodies of water - By law, adulticiding is not allowed near certain bodies of water due to potential environmental contamination. 
3. Inclement weather - Label instructions specify that it is illegal to make treatments with local wind speeds over 10mph or less than 1mph and temperatures below 50 degrees. This is due to the fact that mosquitoes are not active outside of these ranges and without mosquitoes flying in the air the application is useless.

Benefits & Short Falls of ULV Applications:

+/- These applications provides immediate but short term knockdown of adult mosquitoes flying in the immediate vicinity
+/- After about 30 minutes there will be no lasting effect on mosquitoes
+/- Effectiveness is highly variable due to climatic conditions but typically results in an 80% reduction the following night
- Not all areas can be accessed under any particular wind condition
- ULV  spray will only address mosquitoes in the areas which are directly down wind of the truck


- This leaves large areas outside of the spray block untreated especially in rural settings
   •Adult mosquitoes can fly over 15 miles to look for blood meals
   •These products do not eliminate larval mosquitoes 
- Cass County can generally only apply these materials on a weekly basis if thresholds are met
- No truck mounted or ULV application will eliminate every mosquito in an area.


Depending upon time of year and degree of infestation, spray trucks are scheduled to operate between dusk and dawn. Typical mosquito season spray hours are between 7 p.m. and midnight. Applications will occur earlier in evening when temperatures are cooler, specifically in September or October as necessary. 


Cass County employees are directed to drive their trucks during night fogging operations perpendicular to the wind. This allows the product to leave the nozzle of the sprayer and travel down range with the wind. This allows coverage of around 300ft leeward of the truck.

There are situations where trucks will not visit your street directly if the wind is in a particular direction. However this does not mean that you are not receiving the benefit of the application. Mosquitoes can fly over 15 miles looking for blood meals and not all mosquitoes within range of the truck or aircraft will be killed by the spray- but by eliminating enough of mosquitoes the impact of the smaller population is lessened.

In a North wind, roads that run East and West will be sprayed. Houses along the North and South roads will receive treatment as the wind blows the material off the road:

If the winds are from a different direction the same will be true. For instance with a West wind the trucks will spray from down wind to the up wind direction (East to West) spraying North to South roads:

In some circumstances trucks will spray the North and South roads, East and West Roads, and any alley that is encountered if wind conditions allow for dispersal from those routes. For instance if mosquito populations are high, spraying is scheduled over several nights, and winds are NW, NE, SW, or SE this might occur.



If you are a resident in a city/township, or subdivision, please contact your officials to schedule adult mosquito spraying. These applications occur on a contract basis only.