Washington County Arbovirus Management Program, 2009 Pesticide Use Plan Page 1 of 13

WASHINGTON COUNTY

OREGON

DEPARTMENT OF HEALTH & HUMAN SERVICES 

Environmental Health Division 

ARBOVIRUS MANAGEMENT PROGRAM

2009 Pesticide Use Plan 

PART I: DESCRIPTION OF THE ARBROVIRUS MANAGMENT PROGRAM 

The Washington County Arbovirus Management Program was initiated in 2003 in anticipation 

of the arrival of West Nile Virus (WNV) in Oregon, first identified in the United States in 1999. 

The current program is a cooperative effort between Washington County and Clean Water 

Services (CWS), Tualatin Hills Park and Recreation District (THPRD), Beaverton School 

District, and local cities. Participating cities include Beaverton, Cornelius, Forest Grove, 

Hillsboro, Tigard, Tualatin, and Sherwood. Program roles and responsibilities are defined in 

Intergovernmental Agreements (IGA). 

The role of Washington County is to: 

3⁄4 Coordinate efforts to meet the goals of the Oregon Department of Human Service’s 

Public Health Emergency WNV Response Plan. 

3⁄4 Coordinate public health education related to vector-borne disease and mosquito biology 

throughout Washington County. 

3⁄4 Work with state and local agencies to track WNV cases. 

3⁄4 Design and implement a mosquito surveillance program and provide training to IGA 

partner agencies and county staff. 

3⁄4 Provide larvicide product to IGA partner agencies to treat publicly owned sumped catch 

basins. 

3⁄4 Identify mosquito habitats based on surveillance and advise IGA partner agencies of 

appropriate preventative and control measures for properties under the control of the IGA 

partner. 

3⁄4 Identify mosquito habitats in areas of the County not under the control of an IGA partner 

agency. 

3⁄4 Implement mosquito prevention and control measures in areas not under control of IGA 

partners which includes: managing and limiting standing water, promoting the removal of 

decaying organic debris, promoting natural predators, distributing Gambusia affinis, 

treatment of natural water habitat, and treatment of private and publicly owned sumped 

catch basins up to two times per season. 

3⁄4 Maintain a database mapping all identified mosquito habitats, surveillance records, 

complaints, and mosquito control work within the County. 

3⁄4 Process and test adult mosquitoes and dead birds for WNV 
3⁄4 Number and identify species of larval and adult mosquitoes 

3⁄4 Report product treatments to the Oregon Department of Agriculture (ODA) following 

Pesticide Reporting System (PURS) guidelines 

The role of all IGA partners is as follows: 

3⁄4 Utilize and distribute public education materials developed by the County and actively 

educate the public. 

3⁄4 Report mosquito and bird complaints to the County 

3⁄4 Identify and treat publicly owned sumped catch basins within the IGA’s area of control. 

3⁄4 Deliver larval and adult mosquito samples to the County for identification and or testing. 

3⁄4 Implement mosquito prevention and control measures as recommended by the County, 

which includes managing and limiting standing water, removal of decaying organic 

debris, promoting natural predators, and treatment of publicly owned sumped catch 

basins. 

3⁄4 Report product treatments to the Oregon Department of Agriculture (ODA) following 

Pesticide Reporting System (PURS) guidelines 

BUDGET 

This program utilizes resources provided by the County, IGA agencies, and grant dollars. The 

County budgeted $388,000 general fund dollars to this program in the 2008-2009 fiscal year. 

The same level of support is expected for the 2009-2010 fiscal year. Partner organizations 

provide in-kind labor resources. In addition, Clean Water Services provides lab space for 

mosquito identification and WNV testing. Inter-Governmental Agreements (IGA) have been 

renewed through 2011. 

SIZE OF JURSIDICTION 

The County covers 727 square miles. Most program activities are planned to take place within 

the 118 square miles Washington County Urban Growth Boundary (see map 1). The program 

will lay emphasis on prevention and control of mosquito species known to be competent vectors. 

TRAINING 

The Washington County Mosquito Control Coordinator is responsible for training the IGA staff 

in surveillance and control. Training focuses on mosquito biology and ecology, surveillance 

techniques, mosquito species-specific control methods, and arbovirus risks. Training is 

conducted before the start of the mosquito-monitoring season and will continue on an as-needed 

basis throughout the season. The County Mosquito Control Coordinator has completed all 

necessary continual educational hours for recertification purposes. The Coordinator will attend 

trainings when applicable through out 2009. 

 

2008 YEAR END REPORT 

 (See attachment) 

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PART II: SURVEILLANCE 

Washington County and IGA field staff involved with the Washington County Arbovirus 

Management Program conducted active larval and adult mosquito surveillance in 2008. 

Washington County mosquito control workers and IGA field staff inspected 434 potential 

mosquito habitat sites (as shown in Map 2). 

The role of Washington County mosquito control workers and IGA field staff is to: 

3⁄4 Collect mosquito samples for identification and encephalitis testing 

3⁄4 Document surveillance information including: 

 Potential habitat breeding locations 

 Presence of mosquitoes at sites 

 Identified habitat risk 

 Verification of property ownership 

In 2009, the County will continue to identify additional breeding sites and implement appropriate 

prevention and control efforts to minimize mosquito populations located within Washington 

County. 

PART III: MAPPING 

Washington County maps and catalogues: 

3⁄4 Sensitive water areas 

3⁄4 Adult trap locations 

3⁄4 Larval sampling sites 

3⁄4 Mosquito specie distribution and diversity 

3⁄4 Encephalitis case sites 

3⁄4 Dead birds reported and tested 

3⁄4 Gambusia Affinis distribution sites 

3⁄4 Mosquito complaint phone calls 

3⁄4 Surveillance data 

3⁄4 Pesticide usage 

3⁄4 Locations receiving larvicide or adulticide applications (treatments for the year are 

submitted to Oregon Department of Agriculture, as required) 

A map and list of sensitive areas, as identified by the Oregon Department of Fisheries and 

Wildlife (ODFW), located in Washington County has been attached at the end of this document. 

If further documentation is needed for any submitted maps, please contact the County’s 

Environmental Health program. (See attached 2009 Sensitive Areas) 

PART IV: TREATMENT 

Washington County will use Integrated Pest Management (IPM) as an effective and 

environmentally sensitive approach to mosquito management. Washington County will use 

current, comprehensive information on the biology and ecology of mosquito life cycles their 

interaction with the environment. This information, in combination with available control 

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methods will be used to manage mosquito populations with the least possible hazard to people, 

property, and the environment. 

Larvicide selection and time of application will be based on the distribution and behavior of the 

target mosquito species, environment, and weather conditions. Adult vector mosquito control in 

the County will only be conducted in the event of a public health emergency and be based on 

environmental conditions, adult vector mosquito abundance, and/or virus isolation in tested 

mosquitoes, the magnitude of infection in birds, horses, human cases of arboviral disease. 

In 2008, larval vector mosquito control activities primarily focused on publicly and privately 

owned sumped catch basins within the Washington County Urban Growth Boundary (see map 1) 

and high-risk natural water habitats. 

There are approximately 23,230 sumped public catch basins in Washington County with a high 

potential to breed mosquitoes. In 2008, Washington County and IGA field staff treated about 

21,975 sumped public catch basins and 1,267 private catch basins with Altosid XR briquettes. It 

is anticipated that the number of treated catch basins will remain the same or increase as more 

sumped public and private catch basins are identified. 

Refer to the attached 2008 Year-End Report for detailed information regarding vector mosquito 

control activities conducted at sumped catch basins and natural water habitat by Washington 

County and IGA field staff. 

In 2009, Washington County will continue to follow the Oregon Department of Human Services 

Public Health WNV Emergency Response Plan to respond to different West Nile Virus threat 

levels at natural water habitats based on local surveillance findings. Response will be based on 

cases of arbovirus illness detected in the County, vector mosquito abundance, environmental 

conditions and habitat, weather, and the proximity of detected vector mosquitoes to densely 

populated areas within the County. 

In 2009, the County anticipates routine surveillance and larvaciding at sumped catch basins, 

water quality facilities, and natural areas within Urban Growth Boundary. The County will 

increase knowledge related to mosquito species and breeding sites within the County through 

adult and larval surveillance. 

Areas inspected, monitored, and treated in 2009 will be mapped and recorded. Adulticiding will 

be used only in the event of a public health emergency. All adulticide and larvicide applications 

will be documented in the County’s database. Updated maps containing new site locations will 

be submitted to ODHS and ODFW each season and when requested. 

Pesticide applications and other records will be maintained in the County database and in a hard 

copy filing system. 

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PART V: USE OF SURVEILLANCE TO DEFINE THE PROBLEM AND 

 DETERMINE PESTICIDE OF CHOICE 

Larval Surveillance

Standard 4-oz dippers will be used to conduct surveillance of mosquito larvae and pupae. 

Washington County mosquito control and IGA field staff will sample aquatic sources including: 

natural and manmade wetlands, ponds, sumped catch basins, drainage ditches, canals, and other 

standing water using standard 4-oz dippers. The County Mosquito Control Coordinator and/or 

trained staff will identify species and population numbers in submitted samples. 

The threshold to determine treatment will be one mosquito per dip for species with high capacity 

to vector arbovirus for example, but not limited to, Culex tarsalis, Culex pipiens, and Culex 

stigmatasoma. Five (5) mosquitoes per dip will be the standard threshold to determine treatment 

for species with a low capacity to vector Arbovirus for example, but not limited to, Aedes 

vexans, Coquillettidia perturbans, and Culiseta inornata. 

Washington County, for the most part, will limit control activities to mosquitoes species 

identified as potential vectors of arbovirus. If additional potential vector mosquito species are 

identified they will be targeted for control as needed. 

In 2008, sumped catch basins were treated with Altosid XR, which inhibits larval mosquitoes 

from emerging from the pupae stage. A set number of sumped catch basins are monitored for 

efficacy and residual time to determine if and when additional treatment is required. Other 

mosquito breeding sites will be treated with VectoLex CG, Vectobac G, Altosid Pellets, Agnique 

MMF or Golden Bear based on surveillance findings. In these areas, a subset of the sites will be 

periodically monitored 24-72 hours after treatment, to determine a follow up treatment schedule 

and to monitor product effectiveness. 

Evaluating efficacy of treatment

A representative number of sites treated for mosquito production will be sampled 24-72 hours 

post-treatment using standard measures. The number and developmental stage of larval 

mosquitoes sampled will be compared with pre-treatment numbers for that site. A representative 

number of sumped catch basins treated with Altosid XR (Methoprene) will be sampled 24-72 

hours post-treatment and every two (2) weeks thereafter. Live pupae samples will be collected 

and transported to the lab to determine efficacy. 

Non-target effects

Washington County will rely on published scientific materials as well as label directions to 

minimize the impact on non-target organisms. Washington County Arbovirus program does not 

have the capacity at this time to conduct and analyze impacts on non-target organisms. 

Washington County will rely on published studies of non-target effects to determine larval 

control strategies. 

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Documenting sampling results for annual report: 

Larval sampling results are maintained in the County’s database and hard copy files. 

Information includes the species, stage, instar (where applicable) and number of mosquito 

specimens collected in each location. All mosquito collection information will be included in 

the Year-End Report and sent to ODHS and IGA field staff involved in mosquito collection as 

needed. 

Adult Surveillance: 

Adult mosquitoes will be monitored using Carbon Dioxide (CO2) baited Encephalitis Vector 

Surveillance (EVS) traps and Gravid traps. The County Mosquito Control Coordinator and/or 

trained staff will identify species and populations numbers in submitted samples. Adult 

surveillance will be conducted from May through October. Testing for West Nile Virus will be 

done using the Rapid Analyte Measurement Platform (RAMP) in the County lab and/or sent to 

the Oregon State Public Health Lab for testing, as needed. Public complaints may be used to 

determine trapping locations but will not be used to determine adult mosquito control actions. 

Sampling pre-treatment 

3⁄4 To determine species 

Many areas in Washington County are monitored for adult vector mosquito populations 

by County staff and IGA field staff, using Carbon Dioxide (CO2) baited EVS traps and 

Gravid traps. In 2009, Washington County will be increasing the number of adult trap 

sites in the County. CO2 baited EVS traps and Gravid traps will be placed in selected 

areas to monitor adult mosquito activity. Data collected from mosquito samples will 

include species identification, number present, and test results, if done. 

3⁄4 To determine population density 

Trapping adult mosquitoes will provide useful geographic information regarding the 

population density and species diversity of mosquitoes within the urban and non-urban 

areas of the County. Larval surveillance results will be used to determine population 

densities for species that are not readily attracted to adult surveillance measures. 

3⁄4 To determine need for control 

As previously noted, adult mosquito management will be based on cases of Arbovirus 

detected in the County, vector mosquito abundance, environmental conditions and 

habitat, and/or the proximity of detected vector mosquitoes to more densely populated 

areas within the County. 

Sampling post-treatment

3⁄4 To determine the efficacy 

adult mosquito traps will be placed in a select number of sites pre and post-treatment. 

Trapped pre-treatment mosquitoes will be placed in the targeted adulticiding area and 

then collected after the treatment application. The trapped mosquitoes will act as a 

“control group” to give an accurate calculation of the effectiveness of the treatment. 

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3⁄4 Efficacy, In-migration and Non-target effects 

At this time, Washington County does not have the capacity to monitor for pesticide 

resistance, in-migration, or effects of non-target organisms in more depth. To determine 

the proper control method for each situation and to minimize the impacts on non-target 

organisms, the County will rely on proper application techniques and published, 

scientific, and peer reviewed publications. 

Document sampling results for annual report

Adult sampling results are maintained in the County’s database and hard copy files. Information 

includes the species and number of mosquito specimens collected in each location as well as any 

WNV RAMP and Oregon State Public Health Lab testing results. All surveillance information 

will be included in the Year-End Report and periodically sent to ODHS and appropriate IGA 

field staff. Information collected during the mosquito season will map potential breeding sites, 

target larvicide applications and arbovirus transmission risk. 

Choice of Pesticide(s) 

Larvicides: 

3⁄4 Altosid Pellets 

3⁄4 Altosid Water Soluble Pouch (WSP) 

3⁄4 Altosid Briquets 

3⁄4 Altosid XR Extended Residual Briquets (insect growth regulators (IGR)) 

3⁄4 Vectobac G 

3⁄4 VectoLex CG 

These larvicides have been chosen because they are biological pesticides, which release 

chemicals produced naturally and effectively control mosquito larvae populations. These 

products are known to have limited impacts on non-target organisms. Vectobac G and VectoLex 

CG will be the only larvicides used within a sensitive area as determined by Oregon Department 

of Fish and Wildlife. Agnique MMF or Golden Bear will be applied for pupae control if vector 

mosquito breeding areas show that the developmental stages of larvae have surpassed the ability 

to be controlled by the above listed larvicide products. Agnique MMF and Golden Bear will be 

used only as a surfactant to control pupae. 

Adulticides: 

3⁄4 Anvil 10+10 ULV 

3⁄4 Pyrenone 25-5 Public Health Insecticide 

3⁄4 Scourge Insecticide 

Anvil 10+10 ULV a Synthetic Pyrethroid will be used for adult control around populated areas. 

Anvil 10 + 10 will be considered first if adulticiding takes place. Pyrethirins such as Pyrocide 

Adulticiding Concentrate and Pyrenone 25-5 Public Health Insecticide will be the second choice 

of use for populated areas. Although Pyrenone 25-5 Public Health Insecticide is among those 

that will be first considered for adult control, preventing applications directly to water or to areas 

where surface water is present will be closely monitored. As noted on the label, this restriction 

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applies to “wetlands, ditches, irrigation canals, and any surface water areas that drain to or are 

connected either directly or by pumps to lakes and streams.” Scourge Insecticide with 

Resmetherin and Piperonyl Butoxide 18% + 54% may be used where there is an increased 

likelihood of OP resistance in the mosquito population, or where Pyretherin may not be 

effective. Scourge is highly toxic to fish and will not be directly applied to water, or areas where 

surface water is present, or areas where drift and runoff from treated sites may be hazardous to 

fish in adjacent waters. Adulticide products will be applied using ULV applications through a 

contracted source. It has been noted that the adulticides listed above have warnings against the 

use in waterways. Therefore, Washington County will strictly adhere to these requirements and 

use extreme caution at all times when near or around water sources. 

PART VI: MOSQUITO MANAGEMENT 

Larvae Control

The purpose is to minimize disease transmission and the need for adulticide applications by 

managing vector mosquito populations before they become adults. To date, larvae mosquito 

control applications in Washington County include publicly owned storm water management 

structures, bio-swales/retention ponds, backyard habitat (when needed) and natural water 

habitats in the County. Established thresholds (previously noted) are in place based on a 

mosquito’s ability to transmit arbovirus disease (primarily West Nile Virus). The mosquito 

species targeted in disease transmission (primarily West Nile Virus) may change, as more 

information is made available. Established thresholds are subject to change as updated scientific 

information becomes available. Use of larvicide for control will be used when other options (i.e. 

source reduction, education, vegetation management) have been evaluated and/or attempted. 

Products used to control larval mosquitoes will be selected based on characteristics of the site 

including, but not limited to: organic concentration, species present, developmental stage of 

larva, length of control time desired, water hydrology, presence of vegetation, and time of year. 

 

Source reduction

The program will place emphasis on source reduction prior to a larvicide application to reduce 

overall pesticide usage in the environment. This will include, but is not limited to, vegetation 

management, ditch and catch basin cleaning, removal of water flow obstructions with land 

owner/management approval and the reduction or removal of mosquito habitats on residential 

property such as un-maintained swimming pools, birdbaths, old tires, buckets, and clogged 

gutters. 

Biological agents

Gambusia Affinis 

Washington County will distribute Gambusia affinis (Mosquito fish) to residents of the 

County for mosquito control in aquaria. Washington County enforces ORS 498.222, 

which allows Mosquito fish to be stocked only in aquaria; defined as self-contained 

systems that are not fed or drained by natural waterways such as ornamental ponds and 

stock troughs. ORS 498.222 states, “Natural waterways include creeks, streams, sloughs, 

ponds, lakes, and ditches if connected to natural waterways. 

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Bacillus thuringiensis var. israelensis (BTI) 

BTI (product name Vectobac G) has the capability to control a wide range of mosquito 

species with a very low impact on non-target species, making this larvicide an important 

product for tactical control of mosquitoes in Washington County. Bti can be applied to a 

wide range of water areas. Vectobac G will be used to control first through third instar of 

mosquito larvae. 

Bacillus sphericus (BS) 

Bacillus sphericus (product name VectoLex CG) has the capability to control a wide 

range of mosquito species with the exception of Anopheles spp. VectoLex CG is well 

suited for wetland areas and waters with high organic content such as wastewater and 

dairy lagoons. This product has the ability to provide residual control of mosquito larvae 

up to four weeks. VectoLex CG will be used to control first through third instar larvae. 

Methoprene 

Methoprene (product name Altosid) is an Insect Growth Regulator (IGR) that does not 

directly kill larvae mosquitoes, but disrupts the immature larvae stages preventing the 

larvae from developing into adult mosquitoes. Methoprene will be used in the form of 

Altosid primarily in catch basins, storm water facilities, ditches, and tires. In 2009, the 

County and IGA partners will begin treatment of public sumped catch basins in June to 

ensure control throughout the mosquito season. 

Chemical Agents

Agnique or Golden Bear may be used if other products used were not effective and mosquitoes 

are in their pupae stage. The decision to use Agnique or Golden Bear will be made based on 

mosquito species and if the number of pupae present is greater than five (5) per dip. 

Adult Control

To date, adulticide applications have not been conducted in Washington County. In the event of 

a public health emergency, adult mosquito control in the County will be based on cases of 

arbovirus illness detected in the County, vector mosquito abundance, environmental conditions 

and habitat, and the proximity of detected vector mosquitoes to more densely populated areas 

within the County. If an arbovirus is detected in the County, adult samples collected will 

indicate vector mosquito presence and density as well as infected mosquito presence to 

determine which areas have mosquito populations with an increased capacity to vector arbovirus 

in humans (if applicable). 

Adult trapping will take place in selected areas before an adulticide treatment is applied. The 

mosquitoes trapped from the selected location will be placed in the targeted adulticiding area. 

The mosquitoes placed at the adulticide application area pre-treatment will be collected posttreatment to determine efficacy of the application. Pre and post-treatment trapping collection 

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may be done to help determine if the adulticiding was effective, and to help eliminate skewed 

findings that could be caused by in-migration. 

Washington County will make every effort possible to minimize effects on non-target organisms 

using proper adulticide application techniques including rate, droplet size, and atmospheric 

conditions in accordance with label recommendations and published literature. Adulticide 

products will be applied using Ultra Low Volume applications. In the event that an arbovirus is 

detected in the County, contracted services will apply adulticide products to areas of concern. 

If West Nile Virus becomes a threat that surpasses the ability to control adult vector mosquito 

populations by ground using ULV applications with pickup trucks, then aerial applications may 

be considered. A contract is established with Adapco Mosquito Control for aerial applications. 

(See attached 2009 Control Agent Worksheets.) 

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PART VII: PUBLIC EDUCATION AND AWARENESS 

Washington County provides bilingual education materials. Information will be provided to 

local schools, day cares, senior centers, hospitals, healthcare facilities, city resource centers, 

libraries, kennels, and feed stores through out 2009, as requested. The County has prepared 

brochures with information on West Nile Virus for public distribution. The County also 

provides information on the Washington County website. Technical staff presentations and 

educational displays are available upon request by the County Environmental Health Program 

Educator and Mosquito Control Coordinator. 

General Public Notification 

3⁄4 Distribution of a West Nile Virus informational brochure and bookmark developed to 

educate the community on ways to reduce mosquito populations as well as to provide 

information on reducing the risk of mosquito bites. This brochure will be distributed to 

school districts, day care centers, senior centers, hospitals, health care facilities, city 

resource centers, libraries, and kennels as needed through out 2009. 

3⁄4 General information is available on the Washington County website. 

Multi-media Resources

3⁄4 West Nile Virus prevention and vector mosquito control information is available on the 

Washington County website to provide information to the public. Additional federal and 

state educational resources are provided as links at this site: 

http://www.co.washington.or.us/deptmts/hhs/env_hlth/vector/msqt_idx.htm

3⁄4 The Washington County Animal Shelter currently has mosquito control brochures 

available for customers and directs the community to our website for more information. 

3⁄4 A bilingual (English/Spanish) press release regarding West Nile Virus and suggested 

measures to be taken by the public to reduce exposure to mosquito bites was created and 

released to local newspapers in 2008. This is projected to take place again in 2009. An 

information helpline is available in English and Spanish for the public regarding West 

Nile Virus year-round. 

Presentations to Schools, Church Groups, Civic and County Organizations

3⁄4 The Environmental Health Program Educator and Mosquito Control Coordinator will be 

available to give presentations and for community events throughout the year. 

3⁄4 Presentations on mosquito biology, prevention and control are advertised through the 

"Let's Talk about It" communications section on the County’s website. 

3⁄4 The Environmental Health Division will host a booth at the 2009 Washington County 

Fair, which provides information and interactive games for West Nile Virus education. 

The booth will provide an avenue to target a large public sector which might not 

otherwise be reached. Other resources and the availability of Mosquito fish will also be 

highlighted. 

Display Educational Materials at Events

Display materials, brochures, and other educational resources are available for use year-round at 

community events, fairs, and presentations. An education wheel has shown to attract attention to 

Washington County's West Nile Virus booths while engaging the public. 

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