Journal of the American Mosquito Control Association, 12(2):342-352, 1996

THE USDA FOREST SERVICE PESTICIDE SPRAYBEHAVIOR AND APPLICATION DEVELOPMENT

PROGRAM-AN OVERVIEW

JOHN W. BARRY

USDA Forest Service, 2121-C 2nd Street, Suite 102, Davis, CA 95616

ABSTRACT, The USDA Forest Service, even though a minor user of pesticides, has maintained anactive program for understanding the performance, atomization, evaporation, efficacy, environmental fate,atmospheric dispersion, and environmental impact of chemical and biological insecticides. Since its self-imposed ban on use of dichloro diphenyl trichloroethane (DDT) in 1964, the USDA Forest Service haspursued insecticides that are less persistent and have reduced potential for impact on nontarget organisms,application technology that supports their efficient and efficacious use, and computer models that predictinsecticide fate in the environment. This program has been active over the last 3 decades, beginning withresearch for chemical insecticide substitutes for DDT progressing in time to biological insecticides andother biorational control agents. In our effort to make the less persistent insecticides work under forestryconditions, it was necessary to investigate insecticide monitoring, detection, and sampling methods; ap-plication systems; atmospheric influences; tank mixes and adjuvants; nozzles and atomization; evapora-tion; spray deposition and canopy penetration; biological response; and environmental fate. This paperreviews some of this work that might be applicable to mosquito control.

INTRODUCTION

This paper reviews aerial application technol-ogy activities supported by the USDA ForestService pesticide program over the past 30years. Publications and reports resulting fromthese activities are listed by Skyler and Barry(1995) with current updates. Others, includingthe USDA Agricultural Research Service, theDepartment of Defense, and especially our col-leagues in Canada have made signiflcant contri-butions to understanding the principles and prac-tices of forest spray application technology. Re-quests for their publications should be sent di-rectly to USDA-ARS (409)260-9364, the U.S.Army (801)831-3371, or the Canadian ForestService QO5)949-9461. The New ZealandFor-est Research Institute at Rotorua is conductingapplication research to support aerial applicationof herbicides in forestry. Their library can beaccessed by calling New Zealand 64-7-347-5899.

EARLY USE OF AIRCRAFTIN FORESTRY

Alfred Zimmermann, a German forestet wasgranted a patent in l91l by the Imperial PatentOffice, Berlin, Germany, for use of aircraft toapply a pesticide (Quantick 1985). The patentwas for a technique to apply an insecticide tocontrol forest insect pests, specifically the nunmoth (Lymantria monacha Linn.). Others, re-portedly as early as 1913, suggested the use ofaircraft to disperse pesticides (Johansen 1913,Balch et al. 1955-56).

The first actual use of aircraft to apply pesti-

cides was in August l92l by the State Experi-ment Station of Ohio (USA) in cooperation withthe U.S. Army Air Service. The successful test,conducted at Troy, OH, consisted of applyinglead arsenate dust from a military Curtis JN6biplane to a grove of catalpa trees to control ca-talpa sphinz moth (Ceratomia catalpae (Bdv.))(Neillie and Houser 1922). "fhe test was a suc-cess and demonstrated that theory and practicewere realistic (Bany 1993).

Use of aircraft to dispense an insecticide forcontrol of mosquito larvae was demonstrated bythe U.S. Bureau of Entomology in cooperationwith the U.S. Department of Agriculture(USDA) and U.S. Army Air Service in 1923-24 on an extensive swamp and marsh area nearMound, LA. Paris green was applied by U.S.Army Air Service pilots using a De Haviland 4-B airplane. Reduction of potential malaria-car-rying mosquitoes ranged between 88 and 99Vo(King and Bradley 1925, 1926). The plane hadbeen used for cotton spraying and modified witha metal dust dispenser, another project demon-strating cooperation between the USDA and theU.S. Army Air Service.

From 1936 to 1938 autogiro aircraft wereused to study application and deposition of leadarsenate concentrate in woodlands (Potts 1958).This first use of a rotary-wing aircraft to applya pesticide to trees was followed in the late1940s by helicopter trials in Yosemite NationalPark, USA, to control the lodge pole needle min-er (Coleotechnites milleri (Busck)) with the in-secticides dichloro diphenyl trichloroethane(DDT) and malathion. Results of aerial appli-cation became more promising with improve-

J+Z

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ments in chemicals, techniques, and helicopters(Eaton 1962). While using helicopters to applyDDT for control of a range of insect pests, in-cluding cankerworm, gypsy moth, and pine barkaphid, Craighead and Brown (1946) noted sev-eral advantages over use offixed-wing airplanes;however, the small pay load (95 liters) of theearly models was a disadvantage to forest spray-ing. By the 1960s use of aircraft was well es-tablished in North America as a method of ap-plying insecticides to control forest insects.

RESEARCH DURINGWORLD WAR II

In 1940 the Office of Scientific Research andDevelopment (1946), a National Defense Re-search Committee, was established by the pres-ident to conduct research on a broad range ofscience and engineering problems. The scope ofthis research included:

Micrometeorology and theBehavior of Gas Clouds

General Meteorological PrinciplesBehavior of Gas CloudsField Sampling Methods for Nonpersistent

Gases

Aerosols

General Properties of AerosolsStability of Aerosols and Behavior of Aerosol

ParticlesFormation of AerosolsOptical Properties of AerosolsMeasurement of Particle Size and Size Distri-

butionTravel and Persistence of Aerosol Clouds

Dispersal Systems

Atomization of LiquidsDispersal of Liquid DropletsDispersion of Herbicides

Other

Insect Control-Development of Equipmentfor the Dispersal of DDTWind-Tunnel Studies of Fog Dispersal, Gas

Diffusion, and Flow Over Mountainous Ter-rain

In reviewing these subjects there was an ap-parent concern and need for information on fac-tors that influence smoke and chemical and bi-ological agent application technology. Scoville(1946) discusses insect mortality as a functionof drop size and penetration of sprays into forestcanopies and Rouse (1946) reviews wind-tunnelstudies of fog dispersal, gas diffusion, and flows

over urban and forest settings. Many of thequestions on atmospheric behavior we have to-day were of concern to scientists and engineersmore than 50 years ago. They answered some ofthe questions and provided a legacy of infor-mation that is of interest and helpful today.

For those with an interest in reviewing a sam-ple of other papers reporting on earlier applica-tion technology work that relates to insect vectorcontrol, a few references are provided as fol-lows: Potts (1946)-panicle size of insecticidesand its relation to application, distribution, anddeposit; Lamer et al. (1947)--4eposition and ef-fectiveness of insecticidal aerosols; Latta et al.(1947)-effect of particle size and velocity onaerosols in a wind tunnel on mosquito mortality;Himel (1969)-optimum size for insecticidespray depositst Stains et al. (1969)----cage mos-quito kill up to 2 mi. using a low-volume gen-erator; Murray and Vaughn (1970)-measuringpesticide drift to distances of 4 mi.; Cramer andBoyle (1976)-micrometeorology and physicsof spray particle behavior; Spillman (1976)-probability of drop contact and kill of flying in-sects, with l0-30-pm drops; and Yates et al.(1988)-prediction of spray deposit patterns anddispersion characteristics from aerial applica-tions of Bacillus thuringiensis var. israelensisusing the Forest Service Cramer-Barry-Grim(FSCBG) model.

A MULTIDISCIPLINARYAPPROACH

A partnership between the USDA Forest Ser-vice Missoula Technology Development Center(MTDC) and the USDA Forest Service, ForestHealth Protection, staff has focused on applica-tion of pesticides and related technology sincethe 1960s. ln 197O this partnership was extendedto include the U.S. Army Dugway ProvingGround. Work within this consortium has in-cluded the basic science and engineering ofpes-ticide application, atomization, pesticide sam-pling and monitoring, and pesticide behavior inthe atmosphere (atmospheric movement, depo-sition, impaction, volatilization, and penetrationof pesticides into canopies). The ultimate goal,although not apparent in 1970, was to captureand organize all that was known, as well as anynew information, on these subjects and developa system that could organize and deliver infor-mation, in a practical mannel for use by the fieldpractitioner, researcher, and regulator. The sys-tem would assist the field practitioner in devel-oping aerial spray prescriptions for safe, effica-cious, and economical applications; would serveresearchers in studying application problemssuch as sensitivity of one or more factors on

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cloud movement, environmental fate, and effi-cacy; would serve operators as a platform forextending decision support systems, and forplanning and dose-response predictors; andwould serve the regulator in establishing pesti-cide use guidelines and restrictions.

Application technology is one of the most in-terdisciplinary of the applied sciences and en-gineering (Matthews 1979). Those involved inearly pesticide application technology researchwere ahead of their time in recognizing the needfor a multidisciplinary approach. There is no oneprofessional society dedicated to publication ofsuch papers, although this multidisciplinarywork is more closely associated with the Amer-ican Society of Agricultural Engineers. Paperson application technology and related subjectshave been published in a variety ofjournals, in-cluding Journal of the American Mosquito Con-trol Association, Applied Meteorology, PesticideScience, Journal of Economic Entomology, andEnvironmental Toxicology and Chemistry. Per-haps other applied disciplines have experienceda similar situation.

Simulation models, expert systems, and otherdecision-support systems have evolved in partduring the past several decades to organize, an-alyze, integrate, and utilize the massive knowl-edge and databases. Much of the following in-formation addresses the FSCBG aerial spraysimulation model (Teske et al. 1993) that wasdeveloped jointly by the USDA Forest Serviceand the U.S. Army. The initial development ofthe FSCBG model was done by H. E. Cramer(Cramer and Boyle 1976) and R. Keith Dum-bauld, assisted by their colleagues at the H. E.Cramer Co., Salt Lake City, UT under contractto the U.S. Army and the USDA Forest Service.Keith Dumbauld and Harry E. Cramer (Dum-bauld and Cramer 1978) reviewed their model-ing work in a compendium document on theDouglas-fir tussock moth published by theUSDA (Brooks et al. 1978). Most of the otherpapers by Dumbauld and Cramer are listed inthe bibliography authored by Skyler and Barry( l993) .

The first use of a Gaussian plume model inforestry occurred in 1970. The H. E. Cramer Co.and the U.S. Army used an early version of amodel (Cramer et al. 1972) that later would be-come the FSCBG to calculate the dispersion ofan insecticide cloud. The test was conducted onthe Nez Perce National Forest near White Bird,ID in 1971 (Barry et al. 1974, Dumbauld et al.1975, Waldron 1975).

SPRAY SYSTEMS

In response to interest in small-drop technol-ogy generated by researchers at the USDA For-

est Service, Pacific Forest and Range Experi-ment Station in the 1960s, the USDA Forest Ser-vice developed a pressurized spray system forthe DC-3 Dakota aircraft (Jasumback and Mat-tila 1970). In the early 1970s the Forest Servicecooperated with the U.S. Army Deseret TestCenter, Ft. Douglas, UT to test a portable spraysystem (PWU-5/A USAF Modular InternalSpray System) developed by the U.S. Air Forcefor the C-46, C-47, and C-130 aircraft. After anattempted field test in the Lolo National Forestin 1972 using a C-47 to spray Zectran@, the en-gineering testing was terminated due to projectcancellation by the U.S. Air Force (Taylor et al.1972). A version of the related fire-retardantmodular system is being used by the CaliforniaAir National Guard on C-130 aircraft.

Currently the USDA Forest Service is not de-veloping or testing new aerial spray systems.Generally, existing commercial systems and at-omization devices meet USDA Forest Serviceneeds (Barry 1993). However, performance in-formation is needed from time to time on newpesticide tank mixes and new hardware. In thesecircumstances small-scale testing might be con-ducted.

Aerial application of some biorational agents(e.g., pheromones) may present challenges whenusing existing or new spray devices designed fortheir application (Hall and Barry 1995). TheUSDA Forest Service, however, does not antic-ipate development work on pheromone appli-cators in the near future.

SPRAY AIRCRAFT

Aircraft that potentially may be used for forestspraying are well described in a USDA ForestService publication (Hardy 1987). This publi-cation profiles most of the aircraft that have beenused or have the potential of being used for ae-rial spraying. The book has been distributedworldwide and its technical data has been en-tered into the FSCBG model database. The air-craft wake/vortex descriptors in FSCBG differfor each type of aircraft; thus this database isboth essential and a great convenience to theuser of the FSCBG model. The USDA ForestService has no aircraft of its own that are con-figured for spraying. The agency relies on con-tractor aircraft and occasionally upon theUSAF's C-130H for testing and cooperativecontrol operations on Department of Defenselands (Barry and Ekblad 1983, 1989; Rafferty etal. 1989).

What type aircraft is most suited to forestspraying? The answer of course depends on thejob to be done. The USDA Forest Service has acomputer model titled Computer Assisted Spray

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Productivity Routine (CASPR) (Curbishley et al.1993), developed after the Baltin-Amsden for-mula (Amsden 1960), that predicts the cost ofan aircraft to treat a block using inputs to themodel such as load capacity, turn times, speed,and several other inputs. The CASPR model issuggested for helping managers/operators in se-lecting the most suitable aircraft for a specificjob among those that might be available. Gen-erally, small helicopters are preferred (e.g., Hill-er 728 Soloy or Bell 206 Jet Ranger class) forsmall blocks and larger helicopters and fixed-wing aircraft for larger blocks. The main crite-rion is capability to fly close to the canopy andto deliver the maximum amount of spray to thetarget. Safety is the overriding consideration.

Lane separation (swath width) for variouscombinations of aircraft type, tank mixes, andspray systems are often debated. Applicatorssometimes favor a wider lane separation thanexperience and FSCBG model predictions willsupport. The question is often settled by con-ducting an aircraft field characterization testwhere the aircraft sprays over a line of cardsfollowing procedures recommended by Dum-bauld and Rafferty (1977). With the FSCBGmodel these costly flybys are not technicallynecessary unless the aircraft and atomization in-formation are not available for input.

EQUIPMENT CALIBRATION

Lack of a quality control program character-ized USDA Forest Service spray operations upto the 1970s. Not only were aircraft spraying theforests in a highly variable swath spacing pattern(Barry 1977, Teske et al. 1994a) and excessivelyhigh release heights, in many cases the aircraftwere not even calibrated to apply the properamount of spray. Tony Jasumback, MTDC, wasone of the first USDA Forest Service engineersto work on this problem by providing on-siteengineering equipment calibration consultationsin the 1960s. The problem became more acutewhen the insecticide DDT was voluntarilybanned by the USDA Forest Service and lesspersistent insecticides that required more atten-tion to proper application were substituted. Fail-ure of these substitutes was attributed primarilyto poor application and calibration. There wasno room for error when using the low-persis-tence substitutes. Beginning in 1976 the USDAForest Service began training personnel on air-craft calibration and initiated broad-scale cali-bration checks on most contractor aircraft. Sel-dom was an aircraft, noted to be "ready to goand calibrated," found to be actually properlycalibrated. Application quality, however, hassteadily improved since the late 1970s with ap-

plicators, pesticide technical representatives, andUSDA Forest Service technicians working to-gether to improve quality of aerial application.Better-trained personnel, positive attitudes, con-cern for costs, demands for improved efflcacy, aproactive effort on the part of USDA Forest Ser-vice entomologists, use of new technology, andenvironmental mandates have led to significantimprovements in application quality and effec-tiveness.

WIND TUNNEL ATOMIZATIONSTUDIES

The USDA Forest Service was the primarysponsor of studies at the University of Califor-nia-Davis (UCD), Department of Agriculturaland Biological Engineering, to characterize thedroplet spectrum of spray from nozzles and at-omizers of interest to the USDA Forest Service.The most important input to the FSCBG modelis knowing the number and size of drops beingatomized. Model calculations begin with the at-omization inputs, which are essential to accurateprediction of atmospheric dispersion, deposition,and accountancy. The UCD studies were con-ducted in a wind tunnel where wind velocity,atomization, spray device position, and otherfactors could be controlled and measured. TheParticle Measuring System (PMS) was used tomeasure individual particles as described by Yateset al. (1982a, 1982b, 1983). Results of theUSDA Forest Service-sponsored atomizationstudies were reported in a compendium by Sky-ler and Barry ( 1 991 ) and are part of the FSCBGdatabase. Developing the capability to charac-terize the atomization of spray nozzles and at-omizers was a major breakthrough. Before thiscapability one could only estimate atomizationby using methods subject to considerable error.Since the initial demonstration, already men-tioned, others in academia and private sectorhave constructed wind tunnels to characterizeformulations, spray devices, and tank mixes.Nozzle characterization services are now avail-able for hire in the private sector.

FORMULATIONS ANDTANK MIXES

The USDA Forest Service applies insecticidesboth in ultra-low and low volume sprays usingrotary atomizers such as the Beeco*1r1o (Bee-comist Systems, Telford, PA) and Micronair@(Micronair, Miami, FL). For ultra-low volume,tank mixes are applied undiluted at or below Igallon per acre. Bacillus thuringiensis var� kur-staki (B.t.k.) is the primary insecticide appliedby aircraft, with minor applications of Dimilin@.

346 JounNar or nrr Avenlcal Moseuno Cor.t.I.nor- AssocrarroN Vol . 12 . No.2

Gypsy moth virus and Douglas-fir tussock mothvirus (Hofacker et al. 1980) have been appliedas low volume sprays at l-2 gallons per acre.Ultra-low volume and low volume sprays offerseveral advantages over the diluted and higher-volume tank mixes. Costs are reduced throughless handling, less bulk, and larger payloads interms of treatment area and travel time. Efficacyis increased on a volume-to-volume basis overdiluted sprays because the active ingredient isconcentrated in drops (mostly small drops lessthan l0O pm diam) that reach the intended bi-ological target with adequate toxin to cause mor-tality. Ultra-low volume spray also reduces tank-mix volatilization problems and eliminates theneed for adjuvants, as the formulation containsall necessary additives. Effectiveness of USDAForest Service application programs has beensignificantly increased with improved formula-tion and ultra-low volume application. Joyce(1975), Himel and Moore (1967), and others arecredited with the research in the 1960s and1970s that encouraged ultra-low volume spray-ing.

SPRAY VOLATILIZATION

Evaporation of tank-mix volatiles after atom-ization has been a major concern to all who havebeen involved in aerial application. Both the dil-uent carrier (usually water) and the solvenVdil-uent in the formulation (concentrate that is pro-duced by the manufacturer) are subject to evap-oration. The active ingredient generally is notsubject to evaporation. This becomes paramountin accounting for the fate of material in the at-mosphere. If the material has volatilized, onehas no basis to argue that the mass lost to evap-oration equates to loss or unaccountability of ac-tive ingredient. When fate of the active ingre-dient in the environment is of interest one shouldselect samplers that are efficient in collecting therange of drop sizes that contain the active ingre-dient. This is a challenge given that drops arefalling out as the cloud transverses downwindwhile evaporating at the same time. Volatiliza-tion can be predicted and is a capability of theFSCBG model.

The FSCBG model accounts for evaporationin computing atmospheric dispersion and totalaccountancy of spray (Teske et al. 1994d). Re-cent (Teske, personal communication, 1994) un-published information strongly argues that mostatomized tank mixes evaporate at a rate similarto water-that is, they evaporate until the watercontent is lost. Smaller amounts of nonwatervolatiles will evaporate according to their phys-ical and chemical properties. The FSCBG model

has the capability of handling evaporation of alltypes of pesticide tank mixes.

OFF-TARGET MOVEMENT

Drift has become defined as movement ofspray beyond the intended area target. In spray-ing large target areas, such as when spraying foradult mosquitoes, the area outside the target areacovered by spray might be large. Realisticallywe cannot entirely prevent the movement ofspray beyond target areas. We can, however,manage or "direct it" with existing knowledgeand technology to the point that drift is not sig-nificant.

Behavior of aerial sprays in the atmospherehas been one of the primary focus areas for ag-ricultural spray researchers over the past 25years (Ware et al. 1969, 197O, 1972a, 1972b).Understanding spray behavior became more im-portant with increased concerns about pesticidesin the environment and more aggressive regu-latory actions. The new pesticide labeling re-quirements of the U.S. Environmental ProtectionAgency (EPA) of the 1990s require that off-tar-get mitigation information be specified on pes-ticide labels. This has brought to the forefrontinformation and technology that the USDA andothers have developed on spray management.The USDA Forest Service program, while pro-ducing information on spray behavior in forestryoperations (Markin 1982; Barry and Ekblad1983; Barry 1984b, 1985; Barry et al. 1987,1993), has also emphasized maximization of de-position on the target, thus reducing waste ofpesticide that might move beyond or otherwisebe lost beyond the target area. Cramer and Boyle(1976), Ekblad (1977), and Ekblad and Barry(1984) reviewed the influence of meteorology onpesticide application and spray behavioq notingthe complex relationship among numerous phys-ical and atmospheric processes. The processeswould eventually be addressed by the FSCBGmodel (Teske et al. 1993).

Spray clouds that are colored with dyes andtagged with tracers can be observed visually orby instruments such as lasers. In some studiesthe use of tracers is helpful in qualitativelystudying spray behavior. In ultra-low volumeand low volume spraying we are dependentupon wind to move the spray within treatmentareas to help disperse the insecticide. Some usesof insecticides to control mosquitoes over largeareas depend upon wind to transport and mix thematerial. Wind is also used as an ally in movingthe spray away from sensitive areas. With theFSCBG model coupled to knowledge and un-derstanding of aerial application and spray be-havior, we have the capability to develop spray

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prescriptions that will deliver most of the sprayto the target, safely and efficaciously, while min-imizing off-target movement and potential en-vironmental impact. Technology for trackingand recording spray aircraft has been developedand demonstrated (Teske et al., in press) and isbeing connected to the FSCBG model for real-time monitoring of spray aircraft and the spraycloud. This is a major improvement to monitor-ing spray clouds visually or with laser-type in-struments. The knowledge and tools are avail-able to do the job. The challenge is demonstrat-ing and applying this technology.

WEATHER MONITORING

The USDA Forest Service's experimental andfield programs have used a variety of weathermeasuring instruments and platforms since1970. Harold Thistle at the MTDC. Missoula.Ml is the USDA Forest Service professional onatmospheric science, meteorological data acqui-sition, and other geographical positioning sys-tems (GPS) technologies. Realizing the criticalnecessity of understanding the atmospheric en-vironment of target areas, we usually plan forspecial instrumentation to monitor the weather.In doing so we have experienced both successesand failures. Bob Ekblad, who worked onweather studies and instrumentation needs forspraying, tested and demonstrated the utility ofthe Event Model for Complex Terrain (EMCOT)weather station for surface observation to sup-port Forest Service field projects (Ekblad et al.l99O). This instrument is designed to accept anysensor that emits an analog or pulse of electricaloutput signal (e.g., wind speed, temperature, andrelative humidity). Real-time data can be radio-transmitted to a receiver/computer and plotted toassist in operational decisions. The instrumenthas a mast that extends to 2O.5 ft., althoughhigher masts are available. The station has prov-en its utility on both experimental and opera-tional projects.

SPRAY SAMPLINGTECHNOLOGY

The ability to sample the deposition and airconcentration of insecticide sprays is essential toimproving application technology, conductingsound field tests and safe operational projects,understanding the behavior and fate of sprays inthe atmosphere and target area, and addressingenvironmental concerns. In experimental workthe USDA Forest Service uses various types ofsamplers for quantitative, and in some casesqualitative, assessment of spray movement anddeposit both on target and off target.

Most spray deposit sampling technology usedby the USDA Forest Service has been adaptedfrom that used by the former USDA Bureau ofEntomology and Plant Quarantine where Davisand Elliot (1953) used deposit cards to sampledeposit of oil sprays (Dumbauld and Rafferty1977, Bany et al. 1978). Other spray samplinghas been adapted from the scientists and engi-neers of the U.S. Army and U.S. Public HealthService, who developed numerous devices tosample chemical and biological materials in-cluding gases, aerosols, and particulates in theatmosphere. Some of tbe samplers were de-signed to provide time concentrations and dos-ages (dose/time) data. The samplers are de-scribed by Wolf et al. (1959) and to this day thatpublication remains one of the best referenceson samplers and support equipment.

The Rotorod@ sampler (Edmonds 1972, Ted,Brown Associates 1976), remains one of thesimplest and most reliable samplers available forcollecting both chemical and some biologicalaerosol particles by impaction on small rotatingbars. It is more commonly used to monitor sea-sonal airborne pollen levels. The Rotorod, con-sisting of a metal rod (2 types, U- or H-shaped),is rotated by a l2-Y motor, thus collecting par-ticles by impaction. The U-shaped rod is closeto IOOVo efficient in collecting particles 15-25pm in diameter, whereas the H-shaped rod hasa lower efficiency and is designed to collect l-5-pm-diameter particles. This of course is de-pendent upon maintaining the 2,400 rpm of theRotorod motor. The rods can be assayed micro-scopically for pollen, color tracers, or other dis-tinguishable particles; chemically for the activeingredient or tracer; or biologically when a bi-ological tracer is used (e.g., B.r.t. spores). Wefound the Rotorod to be an excellent samplerduring a spray cloud movement study of B.r.&.in Utah (Bany et al. 1993).

CANOPY AND TARGETDEPOSITION

The USDA Forest Service naturally has aninterest in tree canopies-specifically how spraypenetrates and deposits in various types of forestcanopies. The scope of this interest includeswhat reaches and deposits on the upper canopy,what penetrates the canopy, and what impactson the foliage upon which an insect feeds. TheUSDA Forest Service and its cooperators havesponsored a broad array of studies to investigatethe penetration of spray into both coniferous anddeciduous canopies. A literature search will pro-duce numerous studies, such as those by Barry(1984b), Barry et al. (1984), and Teske et al.(1994a). Early work on penetration of spray into

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a coniferous canopy showed that the small drops(less than 100 pm diam) from low volume ap-plication penetrate tree canopies, whereas largedrops (larger than 100 pm diam) are "scav-

enged" in the upper tree crown (Grim and Barry1976). Ultra-low volume applications, such asused with aerial application of B.t.k. to controlgypsy moth, have been shown to penetrate scruboak canopies and deposit about 3OVo of the ma-terial on the forest floor, with the rernaining7OVodeposited in the canopy (Grim et al. 1992, Teskeet al. 1994b). Large volume spray applied to afoliated almond orchard, with a mean canopyheight of 9 m, had a penetration of l57o of thespray based upon recoveries at ground level(Newton et al. 1989).

The effectiveness and dispersion of herbicidesprays was reviewed by Barry (1984a), whopointed out the need to balance target coverageand off-target movement with drop-size deci-sions. This interest was extended to impactionand deposition studies of the western spnrcebudworm, where Himel and Moore (1967\ re-ported that 93Vo of the sprayed and affected lar-vae had not been contacted by any drops largerthan 50 pm in diameter. This was a significantfinding because 95Vo of the spray mass appliedwas in drops larger than 50-pm diameter. Workreported by others in the USDA Forest Serviceusing different tracer techniques reported thatthe majority of drops found on larvae and fo-liage were less than 50 pm in diameter (Robertset al. 1971, 1976; Bany et al. 1974, 1977, '|,981;

Barry and Ekblad 1978; Bany 1984a, 1984b).Through trial and error the USDA Forest Ser-

vice has learned the techniques of conductingcanopy penetration and foliage deposition stud-ies and has gained some insight into the behav-ior of high, low, and ultra-low volume applica-tions into tree canopies. Results of these studiessupport use of ultra-low volume sprays that de-liver drops in the 20-l0o-pm-diameter size rangeto the target.

ENVIRONMENTAL IMPACT

An active program is maintained by theUSDA Forest Service, National Center for For-est Health Management (USDA Forest Service1995) to study impact on nontarget species frompest management actions and related naturalecosystem functions. Even though B.r.&. and oth-er varieties of Bacillus thuringiensis occur nat-urally in the environment, there is concern aboutadditional application of B.t.k. that might impactnontarget species. Other biorational materials,including insect viruses and fungal agents andpheromones, are being studied for potential use(Hall and Barry 1995). The USDA Forest Ser-

vice and Canadian Forest Service maintain anextensive nontarget insecticide impact database.Some opponents would ban the use of biologicalcontrol agents in forestry, leaving few optionsfor direct control of lepidopteran insects, includ-ing exotics that threaten biodiversity and nativeecosystems.

The FSCBG model is an ideal tool for sci-entists who are evaluating the environmentalfate of pesticides. The FSCBG model can pre-dict distribution of a pesticide on the foliage,ground, and other surfaces, and other modelscan be connected to the FSCBG model to predictthe movement and fate of the deposited materi-als into soil and water systems. As biologicaldose-response data become available we will beable to extend the capability of the FSCBG mod-el to predict mortality. This was the subject of asymposium convened by Barry and Riley(1993) .

SIMULATION MODELS FORENVIRONMENTAL PROBLEMS

The Canadian Environmental Assessment Re-search Council sponsored an excellent overviewpaper (Broissia 1986) on environmental modelsfor environmental impact assessment. This paperreviews the various types of models such as theGaussian type (Pasquill-Gifford), upon whichthe dispersion/dosage part of the FSCBG modelis based, and the Lagrangian type, upon whichthe aircraft wake dispersion of the FSCBG mod-el is based. Included are outlined descriptions ofthe various models and their limitations and ca-pabilities for application to environmental prob-lems. A more recent book on environmentalmodeling (Zannetti 1994) contains several chap-ters on environmental simulation methods in-cluding the FSCBG model (Teske et al. 1994c).Zannetti plans to continue this series of publi-cations on environmental modeline and simula-tion techniques.

DECISION SUPPORT SYSTEMS

Decision support systems (DSSs) are beingdeveloped for resource managers to assist themin making sound decisions within a world en-cumbered with information and options. NewZealand (NZ) (Mason et al. 1991, Mason 1992)has developed a DSS for herbicide selection andalternative control strategies. At the initiation ofthe NZ Aerial Spray Modelling Research Group,a group made up of members from the NZ For-est Research Institute, NZ forest companies,DowElanco, Monsanto, and the NZ agriculturalaviation industry, will be coordinating the de-velopment of a DSS for aerial application of her-

Jrnle 1996 Syttlpostulra: AanosoL Ct-our DvNerrltcs 349

bicides (Richardson and Ray, unpublished data;USDA Forest Service 1994). The USDA ForestService is a cooperator with the Forest ResearchInstitute and the NZ Spray Modelling ResearchGroup in development of the DSS. This DSSwill use the FSCBG model as its foundation. Aspointed out by Richardson, the DSS will be apractical tool based upon solid assumptions thatfield people will use to provide information onpotential environmental impact of herbicides, bi-ological impact on target (and nontarget) ani-mals and plants, and cost of application. In es-sence we will be extending the power of theFSCBG model to predict biological effects, bothwanted and unwanted. Graphic outputs, de-signed for ease of understanding and applica-tion, will show biological response as a functionof dose deposition/exposure and width of bufferstrips needed to protect nontarget areas. Thepracticality of the DSS will virtually ensure itsuse when environmental impact and costs are atissue, which, of course, is nearly always. A de-tailed study plan on development of the DDS isbeing prepared jointly by the NZ Forest Re-search Institute and the USDA Forest Service.

SUMMARY

This paper has reviewed some of the high-lights of the USDA Forest Service's pesticideapplication development and spray behaviorprogram. Research on aerial application tech-nology and spray behavior engaged in by theUSDA Forest Service, Department of Defense,and others position us to apply insecticides toforests in a safe, efflcacious, economical, andenvironmentally acceptable manner. TheFSCBG model is a powerful tool that containsand allows use of what is generally known aboutapplication technology and spray behavior.Technically, we have mastered these subjectswithin the context of current hardware and for-mulations. Transfer of this and emerging tech-nology and training of field personnel in appli-cation and understanding spray behavior, how-ever, fall short of the mark. Today the publiccontinues its demand for protection from harm-ful and damaging insects, but they have fear ofenvironmental contamination and impact. Thus,we must apply all existing knowledge to thechallenges of insecticide application. The USDAForest Service is pleased to share its technologywith insect vector control managers, noting thattechnology transfer and training remain the re-sponsibility of both the scientist and the practi-tioner.

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