CR 44 remains closed at Little Thompson River crossing as bridge replacement is underway.

West Nile Virus and Mosquito Control Policy

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In an effort to reduce the risk of human West Nile virus infection, and with the support of the Larimer County Department of Health and Environment, the Town of Berthoud will spray for mosquito control on August 30 and 31.

Stop the Bite full size

Mosquito Control Safety Update

The issues of West Nile virus prevention and an emergency mosquito control policy are often controversial. The Town of Berthoud is very concerned about protecting its residents from potential infection and also sensitive to the worries some may have regarding mosquito control. 

Berthoud has partnerships with Colorado State University, the Larimer County Department of Health, and Vector Disease Control International to address the problems of both the West Nile Virus and emergency mosquito control measures.

Helpful links to navigate this page:

Introduction to West Nile Virus

West Nile is a serious, sometimes fatal, virus that has been found in Larimer County consistently over the past decade. The virus is transmitted by mosquitoes who bite infected birds and then spread that infection to humans and other animals.

There are no vaccines or treatments for the virus, so the best way to ensure safety is to prevent yourself from being bitten by mosquitoes.

Protect Yourself fullPrevention

If everyone takes preventative measures, the need for activating our control policies will be reduced.

The basics of West Nile prevention include:

  • Drain or dump standing water
  • Dress appropriately (long, loose-fitting clothing)
  • Defend yourself with insect repellant
  • Be aware at dawn and dusk, when mosquitoes are most active

Other preventative measures:

  • Stay clear of long grasses, wetlands, shrubs and grassy shores
  • Repair window and door screens to prevent mosquitoes from entering your home
  • Trim bushes away from the ground to allow for air flow and reduction of dampness
  • Leave dead birds where you find them and call 1.877.462.2911

Town of Berthoud Mosquito Control Policy 

To mitigate the potential effects of West Nile virus on residents, the Town of Berthoud adopted Resolution 16-15 regarding mosquito control spraying in July of 2015. This resolution was updated in June of 2017. 

Vector Disease Control International (VDCI) is the Town's contractor for mosquito control measures. Their role includes treating mosquitoes at the larval stage, trapping mosquitoes and sending for testing at CSU, and activating emergency control measures if necessary.

Larvicide Program

VDCI will devote the majority of its staff and resources to eliminating larval activity for the Town of Berthoud. Larvicide measures include treating standing water for the incidence of mosquito larvae prior to maturation into full adults. It is an important control method because it reduces the overall mosquito population. See map below for larvicide boundary areas.

2017 Larvicide map

Adulticide Program

The Town of Berthoud uses a metric called a Vector Index (VI) to determine when to trigger adult mosquito control measures. If the WNV disease is present, it's imperative to stop the disease cycle as quickly as possible to ensure public safety.

In simple language, a Vector Index is is a number calculated by combining measures of the abundance of Culex mosquitoes (the species that carries WNV) and the rate of infection in those mosquitoes.

In conjunction with Larimer County, the Town of Berthoud has adopted a VI trigger of 0.5 to commence adult control measures.

Mosquito Control Measures

The process for activating adult mosquito control in the Town of Berthoud is as follows:

  • Vector Disease Control International (VDCI) places four traps in town and collects mosquitoes in those traps weekly
  • Traps are sent to Colorado State University to determine the presence of WNV in these traps
  • If the Vector Index (VI) is over 0.5 when averaged between all four traps, adult control operations will commence
  • A minimum of 48 hours notice will be given to the residents
  • City-wide control measures will take place over two consecutive days after 10 p.m., weather permitting

Please note: Residents must opt in to be notified about control measures.

To receive a text regarding West Nile Spraying - Text 'Go Berthoud' to 888777 or to opt-in for Community Alerts & West Nile Virus Notifications sign-up at

Berthoud Spray Zones

  More information:

Learning more



Trap Data Test Data
August 30, 2017 Week 35- August 30, 2017
August 23, 2017 Week 34- August 23, 2017
August 16, 2017
Week 33 - August 16, 2017 
August 9, 2017 Week 32 - August 9, 2017 
August 2, 2017  Week 31 - August 2, 2017
July 26, 2017 Week 30 - July 26, 2017
July 19, 2017
Week 29 - July 19, 2017
July 12, 2017 Week 28 - July 12, 2017
July 4, 2017
Week 27 - July 4, 2017
June 28, 2017
Week 26 - June 28, 2017
June 21, 2017
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Week 24 - June 14, 2017
June 7, 2017

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