Developments in aerial pesticide application methods for forestry

PII:SO261-2194(97)00092-6 ELSEVIER

I:; --

Developments in aerial pesticide application methods for forestry Nicholas J. Payne Natural Resources Canada, Canadian Marie, Ontario P6A 5M7, Canada

Appropriate

application

methods

relation

to ensuring

good efficacy

logical

developments

pertaining

developments application mental

play

Forest Service,

parameter

impact,

research,

including

role in

an important

and also minimising to aerial

pesticide

in the design and characterization

application

impact.

in forestry and rotary

modelling,

zones. Published

pesticide use,

the success of

environmental

of hydraulic

use of spray dispersal

the USC of buffer

1279 Queen Street East, Sault Ste.

Scientific are

and mitigation

by Elsevier

reviewed,

pesticide

Science

both

in

and techno-

dispersal

of pesticide

including systems, cnviron-

Ltd

Keywords: forestry; pesticide; aerial application

Pesticide

Pesticide usage is of considerable practical importance in North American forestry, not only for controlling damage from insects and diseases which affects tens of millions of hectares of forest annually (Anon., 1991a), but also for forest regeneration with the use of herbicides. Areas treated with insecticide and herbicide in Canadian forestry averaged about 633000 and 188000 ha per annum, respectively, between 1990 and 1993 (Anon., 1995). For biologically effective usage, the pest control agent must be delivered to the pest habitat at an appropriate time and in a form that facilitates biological effect. For example, in insect larval control this usually means obtaining foliar coverage at a sufficient droplet density (droplets cm -‘) to ensure that a high proportion of insects receive a lethal dose. Additionally, environmental impact from the pesticide application should be minimised, to avoid compromising other valued aspects of forests, such as biodiversity preservation and recreational opportunities. Pesticide application employs knowledge from a broad range of disciplines. Effective applications depend on many aspects, including the design and performance of the dispersal system and the aircraft, chosen volume and active ingredient application rates, meteorological conditions at the time of the application, the characteristics of the spray mixture, forest canopy state, and timing. Information about research and development pertaining to these diverse aspects is not always effectively transmitted to those most likely to benefit from it, and this hinders the implementation of worthwhile improvements which can increase efficacy and reduce application costs and environmental imoact. This review provides a , synopsis of recent progress pertinent to aerial applications for forest pest management.

dispersal

systems

Developments in atomiser design and quantifying atomiser performance have occurred for the principal atomiser types employed in aerial applications, namely hydraulic and rotary atomisers. Although such atomisers have not changed in their fundamental design, recent equipment changes have provided useful performance improvements and the dropletsize spectra of the sprays produced have been extensively characterised to provide information needed to plan applications. Hydraulic

nozzles

nozzles used on aircraft can provide mists [50 pm 400 pm), depending on orifice type and size, pressure, liquid flow rate, nozzle orientation in relation to the slipstream and air speed (e.g. Table I). They have the advantages of simplicity Hydraulic

Table 1. Hydraulic nozzle performance Hydraulic

Liquid Orientation Airspeed flow rate to airflow (m s -‘) (I min ‘) (“)

nozzle type

Flat fan 8010 Flat fan 8010 Flat fan 80 IO Hollow cone D8-46 Hollow cone D8-46 Hollow cone D8-46 Microfoil ‘02X’ radial Microfoil ‘028’ radial

22 22 45 45 4.5 22 22 II

3.8 3.8 3.8 7.0 7.0 7.0 6.1 6.1

0 90 90 0 90 00 0 0

D;,,, , D:J,
VMD

542 414 260 455 304 442 II00 1370

253 lo.31 I83 hYH I33 408 208 897 I59 Sl2 I98 782 762 1440 II40 1660

aDv,o , and Dv,o9 denote diameters at the 10th and 90th percentile points in the volume distribution

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and low cost. In aerial effect of the high

N.J. Payne

applications,

the

air

shear

speed airstream (approx. lo-50 m SK’) over the hydraulic nozzle affects spray atomisation. Increased relative velocity between the air and spray liquid causes a reduction in the average droplet size and an increase in the driftable fraction of the cloud due to the increased energy available for atomisation (Yates et al., 198.5; Bouse, 1994). Statistical analysis of droplet-size spectrum measurements with hydraulic nozzles has yielded empirical models for the prediction of key parameters, e.g., VMD, over a range of operating conditions (Yates et al., 1985; Picot et al., 1989). Of the hydraulic nozzle types, flat fan and hollow cone nozzles are most commonly employed for aerial forestry sprays. Erosion of flat fan nozzles with usage resulted in increased average droplet size, and emphasises the general need for periodic hydraulic nozzle replacement (Ozkan et al., 1992). A need

to reduce the quantity of easily driftable droplets (diameter < 100 urn) generated by hydraulic nozzles has become apparent with the increased concern over environmental effects from forestry herbicide applications, as phytotoxic effects are highly dispersal systems have been visible. Low-drift developed by using large VMD’s (Yates et al., 1985). Although well suited for soil-applied herbicides, they are not optimum for spray efficacy when dealing with foliar-applied herbicides (Prasad and Cadogan, 1991). Low-drift dispersal systems are not widely used for because aerosols insecticide applications (VMD ~50 urn) or mists (50 urn < 100 urn) are needed to achieve optimum coverage of the insect habitat (Himel, 1969; Barry and Ekblad, 1978). Low-drift dispersal systems can be selected to generate tine or coarse sprays, again depending on the choice of orifice size, liquid flow rate and airspeed (7X& I). Very coarse sprays (VMD- 1000-2000 urn) may be generated at low airspeeds. The Microfoil@ and Thru-Valve@ booms (Waldrum Specialties, Doylestown, PA) were designed for helicopters and fixed-wing aircraft 1990; Payne and respectively (Payne et al., Thompson, 1992) and both have been used for operational forestry herbicide applications, particularly around ecologically sensitive areas. These streamlined boom and nozzle type systems may be fitted with various sets of specialised nozzles, spaced at 15-cm intervals. The nozzles all comprise a number of fine tubes (inside diameter - l-2 mm), grouped in a linear or circular arrangement (Figure f and 2). Design aspects that help to reduce the production of small droplets are the alignment of the liquid flow with the ambient airflow, thereby reducing its shearing effect, and liquid flow restrictors that allow the spray liquid to emerge at a relatively low pressure. An upper airspeed limit (11 m s-r) is stipulated with the Microfoil to minimise spray drift. An earlier low-drift hydraulic nozzle design was the Raindrop@ nozzle (Delevan, West Des Moines, IA), which is an add-on cap to conventional hydraulic nozzles, thereby yielding a compound nozzle with the liquid passing sequentially through a primary and then a secondary orifice (Tharrington et al., 1976).

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Figure 1. Microfoil boom section with ‘060’ nozzle and diaphragm check valve

‘This design provides a relatively low small droplet fraction compared with conventional hydraulic nozzles. Other adaptations to dispersal systems designed to reduce spray drift include air deflectors for use on aircraft equipped with hydraulic nozzles (Womac et al., 1994). These deflectors operate by reducing the velocity of the airstream close to the nozzle and hence the proportion of small droplets in the cloud, which in turn reduces off-target deposit. There is a need to evaluate this equipment in aerial forestry sprays. The CP ‘nozzle (Figure 3; CP Products, Mesa,

Figure 2. rhru-valve boom section with ‘070’ nozzle and integral diaphragm check valve

Forestry application technology: N.J. Payne AR), is essentially a deflector nozzle with the capability of having the orifice size and fan angle easily adjusted to two or three predetermined settings. The ability to quickly adapt the system may provide a useful advantage in operational sprays. This equipment generates a droplet-size spectrum that is within the range provided by other hydraulic nozzles used for aerial pesticide application (Bouse, 1994). Rotary atomisers With rotary atomisers, liquid break-up is initially by centrifugal force, but aerodynamic forces resulting from buffeting by the aircraft slipstream complete atomisation, and therefore affect the droplet-size spectrum. Aerial rotary atomiser designs include those based on a gauze cage (Micronair”’ AU 3000, 4000, 5000 and 7000), perforated sleeve (Beecomist 360), cupped disc (Micron X-l and X- l5), or bristled sleeve (AirBi; Cadogan, 1995). They typically produce mists (SO pm < 100 pm) and fine sprays (100 kern< 400 pm), depending on the flow and rotation rate. An increase in rotation rate causes a reduction in the average droplet size (Ehfe 2). Micronair atomisers are commonly used in aerial forestry applications. The AU4000 atomiser employs a 10, 14, 20 or 30 Mesh stainless steel gauze cage with a diameter of 12.7 cm and length of 7.9 cm (Anon., 1991b), that is actuated by means of slipstream-driven propeller blades. The earlier AU3000 design is similar to the AU4000 except for a longer cage (diameter 12.7 cm, length 15.2 cm), and its performance is also similar (Parkin and Siddiqui, 1990). The AU5000 is a smaller and lighter version of the AU4000 (diameter 10.2 cm, length 7.9 cm), allowing a simpler aircraft mount (Anon., 1984). The AU7000 is lighter and adapted for use on slow-flying aircraft, e.g. helicopters and microlights, and in air-assisted ground machines. Statistical analysis of the droplet-size spectrum measurements with Micronair atomisers has yielded empirical models for the prediction of key parameters, e.g., VMD. over a range of operating conditions (Picot et al., 1989; Parkin and Siddiqui, 1990). An electrically driven Micronair atomiser has been developed for use on aircraft to provide better control of rotation speed and optimise the small droplet fraction (Picot, 1990). The droplet spectrum from a slipstream-driven Micronair changes with airspeed with slower speed decreasing the small droplet fraction and deposit Table 2. Rotary atomizer performance

Atomizer type

Airspeed (m 5 ‘)

Liquid Row rate (I min ‘)

Rotation rate (wet rpm)

VMD (pm)

DC.,) , W.,,v (pm) (pm)

“Dv 0 I andDv.o 9 denote diameters at the 10th and 90th percentile points In the volume distnbution

density. The new design avoids the use of propeller blades that limit rotation speed to prevent blade loss due to centrifugal force, to provide improved performance. Atomiser characterisation As atomisers produce a range of droplet sizes, knowledge of the size distribution is needed to optimise pesticide applications. The droplet spectrum generated by a pesticide atomiser is usually measured with a laser spectrometer, which illuminates the cloud and sizes droplets by imaging or by quantifying scattered laser light. These devices do not require droplets from the spray cloud to be caught, thereby avoiding a possible measurement bias resulting from sampling the cloud. Laser spectrometers are mounted in a wind tunnel (Yates et al., 1985) or on aircraft (Yates et al., 1983) to provide realistic airspeeds. Methodologies for measuring droplet-size spectra used for forestry pesticide applications have been described by Yates et al. (1985), Picot et al. (1985), Parkin and Siddiqui (1990) and Picot et al. (1990), and a summary is given by Picot et ul. (1995). A comparison of the various instruments used for droplet sizing was made by Dodge (1987), and a description of other sizing techniques is given by Lefebvre (1989). An alternative method for characterising atomisers is to measure the droplet-size spectrum by quantifying the numbers and sizes of droplets deposited on Kromekote@ cards or other samplers, by use of a tracer dye (e.g. Cadogan et al., 1986). An advantage of this method is that the measured droplet-size spectrum will more closely represent that deposited on a selected target. However, it can be difficult obtaining representative measurements of the small droplet fraction of the cloud with this technique, due to the low deposition efficiency of small droplets. The spray cloud may only be partly characterised when employing this method. Also, the need to apply a spread factor to calculate airborne droplet-size is time consuming and a source of error. In recent years, investigators have characterised a variety of atomisers for aerial pesticide applications over a range of operating conditions, including Micronair rotary atomisers, flat-fan, flooding fan and hollow-cone hydraulic nozzles, and the Microfoil and Thru-Valve booms (Bouse, 1994; Parkin and Siddiqui, 1990; Picot et al., 1989; van Vliet and Picot, 1987; Yates et al., 1984; Yates et af., 1985). Dropletsize spectra obtained using airspeeds appropriate for aerial applications provide an extensive database for atomiser selection. Some empirical models also allow performance prediction based on operating conditions. Of interest in selecting the atomiser and settings are the VMD of the spray cloud, and for insecticide applications, the volume average diameter (droplet size derived by dividing the total volume of spray by the total number of droplets), or number of droplets generated per second (Payne, 199Sa). When controlling insect larvae with foliar spray applications, the droplet density achieved is of great importance to ensure that larvae have a good chance of incurring a

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Forestry application technology: N.J. Payne droplet before weathering reduces the efficacy of deposits. This makes the rate of droplet generation an important parameter in planning the insecticide spray application. When using foliar-applied insecticides on conifers, the spray volume in droplets with diameters less than 100 urn is of interest, as these sizes contribute most to deposits on needles (Picot et al., 1985). In contrast, the proportion of the spray volume contained in droplets with diameters less than 100 urn is important in selecting herbicide application methods, because reducing the small droplet fraction reduces the potential for spray drift and environmental impact.

Pesticide application methods Application parameters Volume application rate. A significant development in aerial application in forestry has been the trend to lower volume rates to increase operational efficiency. Because of the greater area treated per sortie, this reduction has facilitated more efficient aircraft usage and shorter application times, which are important when dealing with a large-scale control program and a short time window due to insect development or meteorological constraints. In the 1970s chemical insecticides were aerially applied at 1 - 2 1 ha-’ against the eastern spruce budworm, but when Bacillus thuringiensis (Bt) was introduced into forestry, the available product potency (approx. 4-8 billion international units [BIU] I- ‘) necessitated higher volume application rates to achieve the effective dose, which had been set at 20-30 BIU ha-’ (van Frankenhuyzen, 1990; Armstrong and Cook, 1993). Improvements in Bt production have yielded higher potency products (approx. 12-33 BIU 1-l) and enabled volume application rates to return to earlier levels, with concomitant operational efficiencies. A volume of 1.2-2.4 1 ha-’ is practical for aerial applications to control other forest insect pests including the gypsy moth (Lymantria &par) and hemlock looper (Lamhdina fiscellaria) (van Frankenhuyzen et al., 1991; West et al., 1989). Currently, volume rates between 0.5 and 1.2 1 ha- ’ are used for control of a variety of Canadian forest insect pests with Bt and tebufenozide, typically with light fixed-wing aircraft equipped with Micronair atomisers. The trend in aerial herbicide application is also to reduce volume application rates, and in eastern Canada volume rates of 33-47 I ha-’ are typically employed. Spray deposition from a commonly used aerial application method employing a 3.5 I ha-’ volume application rate and a boom and nozzle system with D8-46 hollow cone hydraulic nozzles has been made by Payne (1993) for use in comparing different dispersal systems. Droplet-size spectra. The use of ultra-low volume rates

for insecticide treatments has been accompanied by reductions in the average droplet size. A sufficient number of droplets are required to provide the coverage needed to ensure that larvae have a good chance of contacting spray deposits within a suitably short time period, before appreciable weathering by

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rainfall and sunlight has occurred. ULV applications using sprays with VMDs< 150 nm have provided adequate coverage in both deciduous and coniferous canopies. For example, Et applications to control gypsy moth on oak trees, using such sprays, gave good coverage and insect control (van Frankenhuyzen et al., 1991). In addition, higher proportions of spray deposit were found on the undersides of oak leaves, where early-instar gypsy moth larvae feed (van Frankenhuyzen et al., 1991; Payne et ul., 1996). Effective ULV applications have been made using these droplet sizes to control pine beauty moth and spruce budworm (Joyce and Beaumont, 1978; van Frankenhuyzen, 1990). Atomisers and settings suitable for providing the small droplets required for good recovery and coverage in spruce budworm habitat have been evaluated in wind tunnel studies (Picot et al., 1985; van Vliet and Picot, 1987). The Beecomist 360 and Micronair AU 3000 and 4000 atomisers were all identified as capable of generating optimum spectra, provided a flow rate limit was observed. For example, the AU4000 provides about 47% of the spray volume in droplets with diameters less than 55 urn at release when operated at 9000 rpm and a flow rate of 1.9 I min ‘, compared with only 25% at 7.6 1 min -’ (van Vliet and Picot, 1987). Increased cage rotation rate provided a significant increase in the spray volume in the desired size range, but the ‘safety limit precludes operation at these settings. Swath

width. The swath width or aircraft track spacing is a parameter of practical importance in the design of spray applications. Once the volume and active ingredient application rates have been set and the swath width and atomiser settings provisionally chosen, the deposit pattern from an aircraft is often assessed by quantifying dyed spray deposits on Kromekote@ cards placed on open ground. The Swath Kit (Droplet Technologies, Crystal Lake, IL) is an example of a commercially available system for quantifying spray deposits on flat artificial surfaces, for use in assessing deposition on flat targets. However, such deposit assessments cannot give a direct measure of expected foliar deposits because of the greater surface area in a forest canopy and differences in droplet collection efficiency, although estimates can be made based on the leaf area index. In addition, with incremental spraying methods a single swath does not yield the aggregated deposit expected from an operational multi-swath application. To save time and therefore reduce aircraft cost, the usual operational aim is to have as large a track spacing as possible, while achieving sufficient coverage. The interval between successive swaths affects the evenness of coverage expected from a particular application, and may be quantified by the coefficient of variation (standard deviation/mean deposit). An increase in track spacing will increase deposit variability (Parkin and Wyatt, 1982). Further, the swath positioning in relation to the edge of a spray block is not trivial because the relatively large spray release height used in forestry applications results in a significant horizontal displacement of the

Forestry application

spray from the release position, and the potential to affect untreated margins. An experimental method for measuring offset distances has been described by Crabbe and McCooeye (1988). Alternatively, spray dispersal models (see below) can be used for estimations. Aircrufi height. Aircraft height is a key variable affecting the spray deposit pattern, as an increase in release height will reduce peak deposits and increase downwind deposits (Picot et al., 1993). Aircraft height in relation to an inversion is of particular significance in small droplet dispersal because of the significant effect of atmospheric turbulence on the vertical movement of small droplets, due to their relatively low terminal velocity. If an application occurs in the early morning, when an inversion is eroded by ground heating, the upward movement of small droplets by turbulent diffusion is effectively capped by the weak turbulence in an inversion, thereby increasing the proportion of spray deposited in the treatment area. Conversely, during an evening application when the inversion layer builds from ground level while the air aloft still has a neutral or lapse temperature profile, downward transport of small droplets is retarded by the weak turbulent dispersal through the inversion layer. The occurrence of drainage flows and low-level wind jets that begin to develop around dusk (e.g. Stull, 1988) exacerbate the problem by advecting the small droplet cloud away from the treatment area before it is brought down to the forest canopy. Meteorological qffects. Spray dispersal is affected by meteorological conditions, and wind speed is a key parameter as it affects the rate of cloud advection, and for small droplets their impaction efficiency (May and Clifford, 1967). Thus, in aerial sprays employing small droplets against the pine beauty moth in the Scottish highlands, researchers observed higher foliar deposits and lower ground deposits in trials carried out under conditions of increased wind speed (Joyce et al., 1981). Similarly, in small droplet sprays on jack pine, observed foliar deposits were greater in higher wind speeds (Payne, 1994). The level of atmospheric turbulence is also a key parameter, and this is primarily controlled by the stability of the atmospheric boundary layer. By quantifying the airborne cloud, Crabbe et al. (1994) showed that the stable atmospheric boundary layer with low wind speeds and turbulence, which is usually used for aerial forestry insecticiding, actually resulted in more drift than under unstable conditions with greater wind speeds and turbulence. In fact, a greater proportion of the spray cloud was deposited in the spray block in unstable conditions, rather than the conditions around dawn and dusk when sprays have usually been applied. The methodology and results of field trials to measure wind drift from aerial applications under a variety of conditions have been discussed by Crabbe and McCooeye (1995). The recommended range of meteorological conditions for aerial forestry sprays in Canada have therefore been reconsidered in order to maximise spray deposits within the treatment area. Aerial applications could

technology:

N.J. Payne

be appreciably improved by using conditions with greater wind speeds and turbulence levels than is currently the norm, at least for large-scale operations. This change would increase on-target deposit, lessen drift and also lengthen the narrow time window that results from the use of the low wind speed and low turbulence conditions found near dawn and dusk. An overview of the physical processes involved in droplet dispersal and deposition has been given by Payne effects on spray (1995b); while meteorological dispersal have been discussed by Miller et ul. (1995). Application

planning

The planning of insecticide applications may be facilitated by the use of a systematic method to setting key parameters, such as active ingredient (a.i.) and volume application rates, that is based on information about mode of action, insect behaviour, the characteristics of the substrate to be sprayed, etc. This approach was described by Joyce and Spillman (1978) in relation to the use of fenitrothion against pine beauty moth, and has since been extended to the use of the insect moulting hormone analogue tebufenozide (Mimic@) against the eastern spruce budworm (Payne et al., 1997). In the latter case the pest control agent works primarily through ingestion and the target stage of the insect, third and fourth instar larvae, consume approximately 2.4 needles per day, which is equivalent to a surface area of 1 cm2. The spray application was therefore designed to provide an LDcjS (15 ng) on this area, equivalent to an active ingredient application rate of 23 g ha- ’ with a leaf area index of 5 and a ratio of 3 between silhouette and total leaf surface area. This rate was then adjusted upwards to account for volume losses by drift and understorey deposition, typically 30% apiece. The volume application rate was based on a requirement of 1 droplet per needle, to ensure that insects have a high probability of ingesting a droplet during a day’s feeding. Using an average droplet size in the range observed to be deposited on coniferous foliage (50-100 urn), the volume application rate was then estimated by allowing for leaf area index and ratio of silhouette to total leaf area, droplet losses, and evaporation. Such an approach to planning offers greater reliability for applications, particularly those employing new control agents for which field data are lacking, by ensuring droplet coverage and active ingredient densities are sufficient to provide effective pest control. Planning of insecticide and herbicide applications can also be facilitated by computer-based spray dispersal models, which require data inputs to describe the various physical parameters associated with the spraying operation, such as the droplet-size spectrum, height of spray release, formulation characterisitics and meteorological and plant canopy conditions. There are several models adapted for use in forestry that can be run on personal computers, including the PKBW model (Picot et al., 1986; Wallace et al., 1995) the AGDISP model (AGricultural DISPersal Model; Bilanin et al., 1989) and the FSCBG model (Teske et ul., 1993). Using these

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Forestry application technology: N.J. Payne models it is possible to estimate spray deposit (g cm-*) and the proportion of the cloud remaining airborne at various downwind distances from an instantaneous line source. The PKBW is a Lagrangian model that calculates cloud dispersal by first applying an aircraft wake simulation and then a Markov-chain type dispersal based on the atmospheric conditions, taking droplet evaporation into account. It has been tested with experimental results from aerial insecticide and herbicide sprays carried out under a range of meteorological conditions (Wallace et al., 1995). The AGDISP is also a Lagrangian model that predicts the fate of droplets under the influence of the aircraft wake and atmospheric turbulence, also taking droplet evaporation into account. The FSCBG model uses a two-segment approach, to account first for cloud dispersal by the aircraft wake using the AGDISP model and then by atmospheric diffusion using a tilted Gaussian plume (Teske et al., 1993). Performance of the PKBW, AGDISP and FSCBG models has been compared in a test with data from aerial insecticide applications (e.g. Figure 4a and b; Mickle, 1987). These figures respectively present data from insecticide applications made with a Cessna Agtruck fitted with Micronair AU4000s, and a Grumman Avenger (TBM) aircraft fitted with flat fan nozzles (11010s). Spray release heights were approx. 63 and 45 m, and the line source strength is 1 g rn- ‘; thus in Figure 4a the FSCBG model predicts a peak a.i. deposit of 0.9 mg cmp2 at a downwind distance of 250 m, for every 1 g of a.i. released per metre of spray line. Spray deposits from a rotary-wing application have been compared with AGDISP model predictions (Duan et al., 1992) and foliar deposits from fixedwing applications to an oak canopy with FSCBG model predictions (Anderson et al., 1992). In addition, the FSCBG model has been used in a parametric sensitivity analysis (Teske and Barry, 1993) which illustrated the importance of release height on the fate of the spray, and swath width estimations have been made with the AGDISP model (Teske et al., 1990).

The task of accurately locating and defining an area to be treated can be challenging for a pilot airborne over a forest, due to the lack of unambiguous visual cues, so the use of DGPS offers the potential for worthwhile improvements in the accuracy of applications. Also, the use of on-board microcomputer controlled data loggers enables a record of aircraft position, height, airspeed, liquid flow rates and rotary atomiser rotation rates to be kept (Mickle and Robinson, 1990). This will become more widespread in forest spraying operations, to document applicator

OUNPHY

(a) _

17

AgT with

lo-~~rI1l”‘I”‘I”‘1”” 0 200 DISTANCE

lb)

SPRAY 2.1986 MCRONAIR

400 FROM

600 SPRAY

DUNPtiY SPRAY TBU with 11010

1000

600 UNE

(m)

2.1986

TJET

Avionics Developments in electronics have made satellitebased guidance systems and on-board data logging a reality, and these systems are of potential use in forestry operations. Historically, operational forestry applications in large remote treatment areas were usually facilitated by the use of a light aircraft, which maintained a position above the team of spray aircraft and provided guidance to them. Now that GPS (Global Positioning System) technology, originally developed for the US military, is commercially available (e.g. from Trimble, Sunnydale, CA, or Pestechon, Swanton, VA), it offers a useful improvement to forestry spraying operations, especially with DGPS (differential GPS) which yields very accurate aircraft positioning (approx. 1 m) at a high frequency (approx. 1 Hz). This latter system employs a local transmitter to correct satellite-derived information.

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FSCBC .

lo-’

0

.~‘~~,“‘l”‘I’l’I”‘l 200 400 DISTANCE

FROM

600 SPRAY

800 LINE (m)

\

1000

Figure 4. Comparison of measured and predicted spray deposits from aerial insecticide applications. (a) Cessna Agtruck fitted with Micronair AU4000s. (b) Grumman Avenger (TBM) fitted with 11010 Tjet hydraulic nozzles (*, measured deposit; FSCBG, broken line; PKBW, solid line; AGDISP, broken line; from Mickle, 1987).

Forestry application technology: N.J. Payne

in case of subsequent may become a regulatory requirement. performance

problems,

and

Environmental impact mitigation Buffer zones

An important aspect of pesticide use in forestry concerns environmental contamination from spray applications near human habitation and environmentally sensitive areas such as lakes and streams. A technique commonly used to mitigate local environmental contamination from pesticide applications is the observance of a ‘buffer zone’. This is a strip of land between treated and sensitive areas that is left unsprayed. The potential for pesticide contamination by spray deposition, and hence for environmental damage, decreases with increasing distance from the application. Thus, the provision of an unsprayed buffer zone of suitable width ensures that the amount of active ingredient reaching the sensitive area is sufficiently low that any resulting biological effect is insignificant. Spray dispersal initially transports the active ingredient into the environment, and many physical factors affect the amount of spray deposited downwind of the application. The spray release height, the droplet spectrum at release, active ingredient application rate, meteorological conditions, and the treatment area all influence downwind deposits, and hence the required buffer zone width. For example, the greater the application rate, the larger the required buffer width. Also, increasing the treatment area size increases the required buffer zone width. These aspects have been discussed and a technique presented to estimate suitable buffer zone width by assessing a distance where biological effects are minimal (Payne et al., 1988). This is achieved by predicting deposits at various distances from the treatment area and translating them into biological effect using toxicological data for appropriate sensitive species, to assess at what downwind distance the effects are negligible. This technique has been applied to a variety of pesticide application methods to estimate buffer zone widths needed to protect water bodies (Table 3; Payne et al., 1990; 1991; Payne, 1992). This modelling approach has been employed in Canada in conjunction with the FSCBG spray dispersal model described above for federal regulation of forestry use of the insecticides fenitrothion and tebufenozide, and the herbicide hexazinone.

Table 3. Buffer zone width9 Active ingredient

Aircrxft

type

Cilypho\atc .. .. ..

Rotary-wing .-.

Pcrmcthrin

I:ixcd-wing

lk&wing ..

“For 100 ha applications b Height above canopy

for water bodies

Dispersal system

Release height” (m)

VMD (pm)

Microfoil DX-46 TVB DX-46 AU.5000 AU3000

3 3 IO IO IO IO

3000

IO00 IO0 I so I60 0.5

Buffer zone width (m) 25

7s 50 so 50 IO0

Meteorological

effects

The control of many forest insects, e.g. spruce budworm on conifers or gypsy moth on oaks, requires foliar deposits and any spray deposited on the herbaceous understorey is effectively wasted, and may have an environmental impact. As large droplets in the spray cloud contribute disproportionately to ground deposit, such deposits may be reduced by using a sufficiently fine spray while still maintaining acceptable foliar deposits (Joyce and Beaumont, 1978; Payne, 1994). The proportion of spray deposited beneath a tree canopy may also be markedly reduced by employing higher wind speeds, thereby increasing the efficiency of inertial impaction of small droplets on the canopy, as observed by Joyce et al. (1981) and Payne (1994). Furthermore, the level of atmospheric turbulence, controlled by stability, affects off-target deposit from drift (Crabbe et al., 1994), with greater drift occurring in stable conditions. Aircraft effects

The aircraft flying height or spray release height is an influential variable in spray dispersal, particularly in determining the fraction of the spray cloud still airborne at a given downwind distance. Increasing the spray release height increases the fraction of the spray cloud still airborne at a given downwind distance from the aircraft (Picot et al., 1993), and consequently there is a desire to keep spray release heights low. However, in forestry spraying the hazard presented by individual tree heights exceeding the average tree height, and also the atmospheric turbulence caused by the aerodynamically rough forest canopy, makes for a practical lower limit on flying height that is an appreciable distance above the canopy top. Herbicide applications typically use a release height of 10 m above the plant canopy, which at this stage is low in height; for insecticide applications the release height typically ranges between 10 and 30 m above the forest. Another approach for increasing the proportion of the spray cloud deposited within the treatment area relates to the use of aircraft vortices. The descent of small droplets (DC 100 pm), which have a low terminal velocity (~2.5 cm s- I), may be augmented by the action of the aircraft vortices, which possess a downward motion as a result of the lift given to the aircraft (Wickens, 1980). Vortex lifetime should be maximised in order to maximise their effect in bringing small droplets down to the canopy. The influence of aircraft vortices on spray cloud behaviour has been investigated using a photographic method and also with a light detection and ranging (lidar) system. The photographic study confirmed the effectiveness of vortices in usefully augmenting downward transport of small droplets, particularly in stable boundary layers (Tennankore ct al., 1980). The lidar study involved directing pulses of laser light into the cloud and measuring the intensity and time delay of reflected light pulses. In this study the behaviour of small droplets entrained in the upwind and the downwind vortex from crosswind spray lines was observed to differ (Figure 5; Hoff et al., 1989; Mickle,

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N.J. Payne

applications with large droplets involves the use of wing-tip sails. These reduce the amount of spray carried off-target in small droplets by disrupting the wing-tip vortices that entrain these small droplets (Parkin and Spillman, 1980).

1987 and 1993). The downwind wing showed a tendency to sink more slowly than the vortex from the upwind wing, consequently droplets in the downwind vortex were more prone to wind drift than those entrained in the upwind vortex. The observation was thought to be the result of different vortex decay rates caused by wind shear interacting with the counter-rotating vortices. The effect of differing vortex decay rate on spray deposits was measured by McCooeye et al. (1993), who found that, for a range of atmospheric stabilities, total deposit to 200 m from the upwind wing was, on average, 1.5times that from the downwind wing. The practical utility of this has yet to be fully assessed for forestry applications, but the use of only the upwind part of the dispersal system may be of value when spraying near sensitive areas. An aircraft modification when making spray

Future developments The trend in forestry, as in agriculture, is towards greater use of biological pest control agents such as insect viruses (Cunningham, 1995) and Bt (van Frankenhuyzen, 1990) to take advantage of their specificity and reduced environmental impact. With this trend will come requirements for improved equipment, formulations and application methods, to maximize efficacy. Increased use of GPS for spray

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aircraft guidance, and on-board monitoring of some significant operational spraying parameters also offers the prospect of improved application and regulation of pesticides in forestry. A re-evaluation of the meteorological conditions under which aerial forestry sprays are applied is also appropriate, based on spray dispersal data now available. Finally, the important need to achieve forest pest control with minimal environmental impact will result in the widespread use of mitigation measures, such as buffer zones and specialised dispersal systems.

Duan,

B.. Yendol.

comparison

Emiml.

W.

the

G. and Mierzejewski.

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model

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K. (1092) deposit

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data.

Atnlos.

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M.

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of

technology:

optimum

size

for

insecticide

spray

62, 9lY-Y2S

R., Mickle, R. E. and Froude, F. A. (IYXY) A rapid acquisisystem for aerial spray diagnostics. Truns. ASAE 32,

1523-1528 Joyce, R. J. V. and Beaumont. J. (lY78) Collection of spray droplets and chemical by larvae, foliage and ground deposition. In: Comrol of Pitirle Beauty Moth by Fcwitrodliorl in Scotland 1978, ed. A. V. Holden and D. Bevan. Forestry Commission. Edinburgh, pp. 63-80

References Anderson. D. E., Miller. D. R.. Wang, Y., Yendol, W. G.. Mierzejewski. K. and McManus, M. L. (1992) Deposition of aerially applied Bt in an oak forest and its prediction with the FSCBG model. J. Appl. Metmrol. 31, 1457- 1466 Anon. ( I Y84) Micromir AUS Mini Atomiscr Hundhook. nair Ltd.. Bemhridge Fort, Isle of Wight, UK. 38 pp. Anon. (IYYla) to Parliament.

The state of Canada’s forests Forestry Canada, Ottawa. 85 pp.

IYYI:

Micro-

2nd report

Anon. ( I YY I b) Micronuir AUNIOO atomizer: Operator~s:c.’ Har&ook. Micronair Ltd.. Bembridge Fort, Isle of Wight, UK, 52 pp. Anon: ( I YY5) Compcxdiurn of’ Carludiarl Canadian Council of Forest Ministers, Ottawa. Armstrong. J. A. and Cook. C. A. (1903) Aerial on Canadian forests: lY45-IYYO. Information Canadian Forest Service, Ottawa, 266 pp.

Fores@

Stufisticx.

217 pp. spray applications report ST-X-2,

ASAE (1987) Terminology and definitions for agricultural chemical application: Standard ASAE S327. I. In: Standards, Engineerin$ Practices and Data Developed and Adopted by the American Societv of Agricultural Engineers. ed. R. H. Hahn and E. E. Rosentrcier. So&y for Eniineering in Agriculture, St Joseph, MI. pp. 147-148

Joyce, R. J. V., Schaefer. G. W. and Allsopp, K. (1981) Distribution of spray and assessments of larval mortality at Annabaglish. In: Aeriul Applicariorz of Insecdcide aguinsl Ant Beauty Moth, ed. A. V. Holden and D. Bevan. Forestry Commission. Edinburgh, pp. 15-46 Joyce, R. J. V. and Spillman, J. J. (lY78) Discussion of aerial spraying techniques. In: Control of fine Beatr/y Moth hy Fwitrw /hion if1 Scohnd 1978, ed. A. V. Holden and D. Bevan. Forestry Commission, Edinburgh, pp. 13-20

L. F. (lY94) Effect of nozzle type and operation size. Trans. ASAE 37, 1389-1400

Cadogdn,

hts

B. L. (1005)

Aerial

control

in Canadu. ed. J. A. Armstrong

Resources

Canada,

Ottawa.

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equipment. In: Forest /n.sec/ and W. G. H. Ives. Natural

pp. 537-543

Cadogan, B. L.. Zylstra. B. F., Nystrom, C., Pollock, L. B. and Ebling. P. M. (1986) Spray deposits and dropsize spectra from a high wing monoplane fitted with rotary atomizers. Trans. ASAE 29,

402-406 Crabbe. R. S. and McCooeye. M. (1988) Field procedure for measurement of flightline offset in forestry spraying. Aeronautical Note NAE-AN-S I, National Research Council Canada. Ottawa. Crabbe, R. S. and McCooeye. M. (lYY5) Effect of atmospheric stability on wind drift of spray droplets from aerial forest pesticide applications. In: Forest Insect Pests in Curlada, ed. J. A. Armstrong and W. G. H. Ives. Natural Resources Canada. Ottawa, pp. 4Y7-5 IO Crabbe, R. S.. McCooeye, M. and Mickle, R. E. (lYY4) The influence of atmospheric stability on wind drift from ultra-low-volume aerial forest spray applications. J. Appl. Me/coral. 33, 500-507 Cunningham. J. C. (1995) Insect viruses. In: Foresf Ir~.scc/ fetrs irl Cunudu, cd. J. A. Armstrong and W. G. H. Ives. Natural Resources Canada, Ottawa, pp. 327-340 Dodge. L. E. (1987) Comparison of performance instruments. A/~/II. Oprics 27, 1328-1341

New

io, X3-95 McCooeye, M. A., Crabbe, R. S.. Mickle. R. E.. Robinson, A., Stimson. E. B., Arnold, J. A. and Alward, D. G. (lY93) Strategy for reducing drift of aerially applied pesticides. Institute for Environmental Chemistry, Ottawa, 33 pp plus appendices. Mickle, R. E. (1987) A review of models for ULV spray scenarios. In: Proc. .Qvnp. Aerial Application of Pehides it! Fore.sby’, ed. G. W. Green. AFA-TN-IS, Natl Res. Council. Ottawa. pp. I7Y- 18X Mickle,

R. E. (1093)

Utilizing

Sci. HeaIr

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B29, 621-645

of insccticidc

Bilanin, A. J., Teskc, M. E.. Barry. J. W. and Ekblad, R. B. (1989) AGDISP: the aircraft spray dispersion model. code development and validation. Trarts. ASAE 32, 327-334 Bouse, droplet

and Spruys. Hemisphere.

May, K. R. and Clifford, R. (lYh7) The impaction of aerosol particles on cylinders, spheres, ribbons and discs. AWL Ckc14p. Hyg.

J. Etnhwz. Barry, J. W. and Ekblad, R. B. (1978) Deposition drops on coniferous foliage. Trans. ASAE 21. 4X-440

A/omizu/io,l

Lefcbvre, A. H. (1989) York, NY, 421 pp.

of drop-sizing

Mickle, R. E. and Robinson, A. G. (IYYO) A monitor spraying. ARQD report. Atmospheric Environment Environment Miller, D. atmospheric

Canada.

FHM-NC-07-95. Ozkan.

Ottawa,

R.. Reardon, primer for USDA

H. E., Reichard,

size distributions i’ku7s. AWE 35.

for aerial Service.

I2 pp.

R. C. and McManus, M. aerial spraying of forests. Forest Service.

Morgantown,

D. L. and Sweeney,

across the fan patterns I OY7- I I02

(1995) An Publication WV.

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19 pp. Droplet

of new and worn nozzles.

Parkin. C. S. and Siddiqui. H. S. (IYYO) Measurement of dropsize spectra from rotary cage aerial atomizers. Crop hot. 9. 33-38 Parkin. C. S. and Spillman, J. J. (1980) The use of wing-tip a spraying aircraft to reduce the amount of material off-target Parkin,

sails on carried

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lane separations I, 309-321

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The determination

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Payne, N. J. (1092) Off-target glyphosate applications and buffer zones required

of herbicides.

of Hight-

Crop fro!.

from aerial silvicultural around sensitive areas.

Pestic. Sci. 34, 53-S’) Payne, N. J. (1993) Spray dispersal from aerial silvicultural sate applications. Crop Prof. 12, 463-460 Payne, N. J. (1994) Spray deposits from aerial simulant applications to a coniferous plantation wind speeds. Crop I%/. 13, l2l- I26

glypho-

insecticide spray in low and high

Payne, N. J. (lYY5a) Principles of atomization and atomizer selection. In: Forest hecf Pests in Cunudu, ed. J. A. Armstrong and W. G. Ives. Natural Resources Canada. Ottawa. pp. S21-S2Y

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1998 Volume 17 Number 2

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Forestry application

technology:

N.J. Payne

Payne, N. J. (1995b) Spray dispersal, deposition and assessment. In: Forest Inwct Pests in Cunuda, ed. J. A. Armstrong and W. G. H. Ives. Natural Resources Canada, Ottawa, pp. 465-478. Payne, N. J., Cunningham, J. C., Curry, R. D., Brown, K. and Mickle, R. E. (1996) Spray deposits in a mature oak canopy from aerial applications of nuclear polyhcdrosis virus and Racillm thuringimsis to control gypsy moth Lymantrio dispar L.. Crop /‘rot. 15,425-43 I Payne, N. J., Feng. J. and Reynolds. P. E. (1990) Off-target deposits and buffer zones required around water for aerial glyphosate applications. fmtic. Sri. 30, 18% I98 Payne, N. J., H&on. B. V., Sundaram, K. M. S. and Fleming. R. A. (1988) Estimating buffer zone widths around pesticide applications. /&tic. Sci. 24. l47- I6 I Payne, N. J., Rctnakaran, A. and Cadogan, L. (lYY7) Dcvelopment and evaluation of a method for the design of spray applications: aerial tebufenozidc applications to control the eastern spruce budworm Choristoncura @ntirana (Clem.). Crop Prot. 16, 285-290 Payne, N. J., Sundaram, K. M. S. and H&on, B. V. (1991) Airborne permethrin and off-target deposits from an aerial ultralow-volume silvicultural spray. Crop f’rot. 10, 357-362 Payne, N. J. and Thompson, D. (1992) Off-target glyphosatc deposits from aerial silvicultural applications under various meteorological conditions. fktic. Sri. 34. l-8 Picot, J. J. C. (1990) Liquid spraying. US patent # 4,948.050.

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aerial

Picot, J. J. C., Bontemps, X. and Kristmanson, D. D. (1985) Measuring spray atomizer dropsize spectrum down to 0.5 pm size.

Trans. ASAE 28, 1367-1370 Picot, J. J. C., Kristmanson, D. D. and Basak-Brown, N. (1986) Canopy deposit and off-target drift in forestry aerial spraying: the effects of operational parameters. Trans. ASAE 29, 90-96 Picot, J. J. C., Kristmanson, D. D., Mickle, R. E.. Dickison, R. B. B., Riley, C. M. and Weisner, C. J. (1993) Measurements of folial and ground deposits in forestry aerial spraying. Trans. ASAE 36,

1013-1024 Picot, J. J. C., Kristmanson, D. D. and van Vlict, M. W. (1995) Spray atomizer droplet characterization. In: Forest /n.wct Pests in Cunada, ed. J. A. Armstrong and W. G. H. Ives. Natural Resources Canada, Ottawa, pp. 5 I I-520. Picot. J. J. C., van Vlict, M. W. and Payne, N. J. (1989) Droplet size characteristics for insecticide and herbicide spray atomizers. Can. .I. Chern. Eng. 67. 752-761 Picot, J. J. C., van Vliet, M. W., Payne, N. J. and Kristmanson, D. D. (1990) Characterization of aerial spray nozzles with laser light scattering and imaging probes and flash photography. In: Liquid Particle Size Measmwwnt Techniques: 2nd ~vhmw, ASTM STP 1083. American Society for Testing and Materials, Philadelphia, pp. 142- 150. Prasad, R. and Cadogan, density on phytotoxicity 415-423

B. L. (1991) Influence of three herhicidcs.

of droplet size and Wec,~I TcLhn~l. 6,

Stull, R. B. (1988) An Introduction to Boundary Layer Meteorology. Kluwer, Dordrecht, 666 pp. Tennankore, K., Picot, J. J. C., Chitrangad, B. and Kristmanson, D. D. (1980) Aircraft vortex studies in forest aerial spraying. fians. ASAE 23, 1076-1083

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Parametric

sensitivity

in

Tcske, M. E., Bowers, J. F., Rafferty. J. E. and Barry, J. W. (1993) FSCBG: an aerial spray dispersion model for predicting the f;ttc of released 453-464

material

behind

aircraft.

Environ. T%xico/. and C‘hon. 12.

Teskc. M. E., Twardus, D. B. and Ekhlad, R. B. (1990) Swath width evaluation. Report number Y034-2X07-MTDC. USDA Forest Service Technology and Development Ccntrc, Missoula. MT, 2.7 pp. Tharrington, W. H., Brandenburg, B. B.. Tatc R. W. and Saunders. W. J. (1976) The raindrop nozzle: drift reduction by design. Proc. Southern Weed Science Sot. 29th Annual Meeting, pp. 493-496. van Frankcnhuyzcn,

K.

(I990)

Bacillus thuringi:iensi.sfor control Chron.,

Development and current status of of defoliating forest insects. For.

Oct., 498-507.

van Frankcnhuyzcn, K., Weisner, C. J., Riley. C. M.. Nystrom, C.. Howard, C. A. and Howse, G. M. (1991) Distribution and activity of spray deposits in an oak canopy following aerial application of diluted and undiluted formulations of BaciLw /htmringivnsi~ Berliner against the gypsy moth Lynzantria dispur L.. I+s/ic. Sci. 33. 159-168 van Vlict, terization

M. W. and Picot, J. J. C. (lY87) Drop for the Micronair AU4000 aerial Atorniza/ion and Spray Techrzolo~ 3. I2- I34

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Wallace, D. J., Picot, J. J. C. and Chapman, T. J. (1995) A numerical model for forestry aerial spraying. Agric. FOK Meteowl. 76. 19-40 West, R. J., Rake, A. G. and Sundaram, A. (1989) Efficacy of oil-based formulations of Racill~rs thuringiensis Berliner var. kws/aki against the hemlock looper Larnhdina fisccllaria fiscellarirr.

Con. En/. 121, 55-63 Wickcns, K. (1980) A stream tube concept for lift: with reference to the maximum size and configuration of aerial spray emissions.

Can. Aeronaut. Sci. 26. I34- 14.3 Womac, A. P. R. (1994)

R., Mulrooncy, J. E., Young, B. W. and Alexander, Air deflector effects on aerial sprays. Truns. ASAE 37.

725-733 Yates, W. E., Akcsson, N. B. and Cowden, R. E. (1984) Mcasuremcnt of drop size frequency from nozzles used for aerial upplications of pesticides in forests. Report number 8434 2804, USDA Forest Service Equipment Development Centre, Missoula. MT, 221 pp. Yates, W. E., Cowden, R. E. and Akesson, orientation, air speed and spray formulation spectrums. Trans. ASAE 26, 163% I643

N. B. (1983) Nozzle affects on drop size

Yates, W. E., Cowden, R. E. and Akesson, N. B. (1985) Drop size spectra from nozzles in high-speed airstreams. 7?ans. ASAE, 28, 405-410 and 414. Received 29 October 1996 Revised 9 December 1996 Accepted I1 September 1997