Measurements of Downwind ULV Droplet Profiles under Various Meteorological Conditions1

There is a pressing need to quantify more fully the fate of ULV spray droplets dispersed over agricultural crops. For this purpose, field experiments were performed under various meteorological conditions of wind speed and turbulence level. Quantified atomizers were employed, giving known droplet diameter spectra. Vertical profiles of droplets impacting onto thin cylindrical collectors were measured at many stations up to 160 m downwind and at heights up to 12 m; they are presented in graphical form. They are also compared with available diffusion theories.     

Off-target glyphosate deposits from aerial silvicultural applications under various meteorological conditions

Aerial spray applications of the herbicide glyphosate were made over a forest canopy under various meteorological conditions. A ‘Thru Valve Boom’ dispersal system carried by a Cessna 188 fixed-wing aircraft flying at 49 m s^?1 was used to generate an aqueous spray cloud with a volume median diameter of 150 μm. Glyphosate deposits from multiple overlaid crosswind line sources released at 10 m above ground level were measured on ground sheets and artificial foliage at downwind distances between 50 and 400 m. Trials were conducted in stable, neutral and unstable atmospheric boundary layers with average wind speeds between 2·2 and 5·7 m s^?1 and vertical intensities of turbulence between 0·07 and 0·16. Linear regression lines fitted to logarithmically transformed measurements and downwind distances (x) gave statistically significant correlation coefficients (P = 0·01), and were compared by ANOVA. Glyphosate deposits on ground sheets and artificial foliage were attenuated at rates inversely proportional to x to the power 1·7-4·3. Regression line comparison showed that, in general, deposits on ground sheets decreased with increasing wind speed and intensity of turbulence, and some statistically significant differences were found in slopes and elevations of regression lines from different trials. However, deposits at the 50-m station increased with wind speed due to the large-drop cloud component. Regression line comparison for deposits on artificial foliage showed that, in general, they were highest in the intermediate wind speed-neutral stability case and similar in the high wind speed-unstable and low wind speed-stable boundary layers, although deposits at the 50-m station also increased with wind speed.     

Spray drift as influenced by meteorological and technical factors

BACKGROUND: The objective of this study was to investigate spray drift from a conventional field sprayer as influenced by meteorological and technical factors, and to provide spray operators with data on which to base sound judgements when applying pesticides. The study was conducted in grazing fields and cereal crops. RESULTS: Interpreting the results from 15 field trials under varying meteorological conditions using different boom heights and driving speeds indicates that, during normal spraying conditions, the most decisive factors influencing the total spray drift (TSD) will be boom height and wind speed, followed by air temperature, driving speed and vapour pressure deficit. One important finding was that TSD (within the encompassed range of meteorological conditions and a boom height of 0.4 m) could be expressed as a simple function of the fraction of droplets ≤ 100 µm. In cereal crops: TSD = 0.36 + 0.11× [fr. (d ≤ 100 µm)] and in grazing fields, TSD = 1.02 + 0.10× [fr. (d ≤ 100 µm)]. In most cases a fraction of the airborne drift passed over the 6 m sampling mast located 5 m downwind of the spray swath. CONCLUSIONS: Under specified conditions, the present results indicate a simple relation between the total spray drift and volume fractions of droplets ≤ 100 µm. Given the nozzle type, it was concluded that the most decisive factors determining TSD are wind speed and boom height. Evaluating the relative importance of the meteorological and technical factors contributes to increasing knowledge in this field of research. Copyright © 2011 Society of Chemical Industry     

Addition of Oil to Pesticide Sprays—Downwind Movement of Droplets

Abstract

An investigation of the downwind movement, distribution and distance covered from a spray source of insecticide to which oil is an additive. Vertical targets were placed at distances ranging from 0.25 to 64 m and at three heights, 35, 70 and 150 cm, downwind from the spray source. There was an increase in the number of droplets arriving at the targets when 20% oil was added to the aqueous solution. An even greater increase was seen when oil only was sprayed; these results are compared with sprays containing water and a 5% wetting agent. Droplet size and air turbulence effects are discussed, as is the faster evaporation of water-based sprays. The work was carried out on rhododendron leaves using Saturn yellow fluorescent dye as a tracer using a Micron Mini-ULVA and Ulvapron oil. A comparison is made with the use of Shell oil A and Risella 33 used by pest workers.     

A Rapid Method of Calculating the Downwind Distributions from Aerial Atomisers1

There are many diverse views about the effects of wind on aircraft sprays. Some operators wish to spray only when the air is still, others will not spray unless the wind speed is at least 3 m/s. The basis of this difference is the fear of, as against the use of, the downwind movement of droplets. This note uses a simple model of droplet behaviour in a wind to try to predict the deposit distributions downwind of a spraying aircraft. The results demonstrate that the level of turbulence caused by the wind blowing over the earth's vegetation reduces the downwind distance most small drops travel before being captured. Trees create more turbulence than cereal crops, which create more turbulence than bare earth or short grass. The deposit density at a given distance downwind reduces with decrease in aircraft flying height, wind speed and smoothness of the canopy. It remains roughly constant with increasing droplet size until a critical diameter is reached when it falls rapidly with increase in droplet size. This critical size depends upon windspeed and turbulence intensity. A downwind buffer zone between the spray area and a sensitive crop is desirable and its minimum size can be determined using the techniques discussed in the paper.     

A method of investigating the effect of droplet size on pesticide collection by vegetation

A new technique is described which allows an estimation of the relative collection of insecticide on a crop, for three discrete droplet sizes simultaneously. Three droplet clouds, each consisting of a different chemical, were released along a line perpendicular to the wind. Subsequent chemical analysis of vegetation samples showed the relative efficiency of capture by any part of the plant as a function of the droplet size. The target vegetation and the micrometeorological conditions were the same for all three droplet clouds and thus did not mask the effects of droplet size. Initial results for a young crop of irrigated cotton are presented. The downwind distributions of chemical residues were in good agreement with a theoretical model published by Bache and Sayer.     

Periodicity and gradients in dispersal ofAlternaria linicola in linseed crops

Conidia ofAlternaria linicola produced on infected linseed crops were mainly dispersed by wind. The numbers of conidia in the air above linseed crops collected by a Burkard spore sampler were greatest between 1200 h and 1300 h, when the relative humidity was lowest. Although numbers of conidia collected decreased with increasing height within and above the crop canopy, air-borneA. linicola conidia were present up to 80 cm above the crop canopy. Conidia ofA. linicola were transported by wind up to at least 40 m downwind from an artificial line inoculum source, but their numbers decreased with increasing distance from the source. In 1991, 1992, and 1993, the dispersal ofA. linicola conidia above linseed crops followed a seasonal periodicity which was influenced by weather conditions and cultural practices. The greatest numbers of conidia were collected during July, August and early September and coincided with periods favourable for sporulation and with an increase in the incidence of the disease in the senescent crop. Air-borneA. linicola conidia produced on point or line inoculum sources (naturally infected linseed stem debris) were responsible for the spread of the disease in linseed crops. In 1992 and 1993, the disease was first detected downwind from the sources, but by the end of the growing seasons, it had spread in all directions and up to 20 m and 60 m from the sources, respectively. Disease gradients were initially steep near the inoculum sources but they became flatter with time due to the secondary spread of the disease.     

Off-target glyphosate from aerial silvicultural applications,and buffer zones required around sensitive areas

Off-target glyphosate deposits were measured downwind of aerial silvicultural applications which used D8-46 hollow-cone hydraulic nozzles, ‘Micronair’ AU 5000 rotary atomisers, and the ‘Thru Valve Boom’ (030), with volume application rates of 35, 20 and 20 litre ha^?1 respectively, and a glyphosate application rate of 2·1 kg ha^?1. Crosswind spray lines were released 10 m above ground level over a short forest canopy, from a fixed-wing aircraft flying at 45 m s ¹ in atmospheric boundary layers with average wind speeds and air temperatures of 2·2-3·7 m s^?1 and 8-23°C at release height. Ground sheets and artificial foliage clusters were exposed at downwind distances of between 50 and 300 m. Glyphosate deposit measurements at various downwind distances (x) were fitted with non-linear regression lines; deposits were attenuated at rates inversely proportional to x at powers of 1·3-2·3. For a particular trial, deposits on ground sheets and artificial foliage were generally similar, and ranged between 19 and 0·04 mg m^?2 over the sampling distances used. For 100-ha applications the estimated buffer-zone widths around water bodies were less than 50 m, whereas those around non-target vegetation ranged between 75 and 1200 m, depending on the application method and the meteorological conditions.     

Field electroantennogram and trap assessments of aerosol pheromone dispensers for disrupting mating in Epiphyas postvittana

An electronically controlled aerosol system for mating disruption was evaluated against Epiphyas postvittana Walker in apple orchards in New Zealand. The area in which male moths were affected by the aerosol system was examined using catches in traps radiating from a central single-point source of either one aerosol can dispenser or 100 polyethylene tubing dispensers, compared with catches in orchard plots without pheromone dispensers. Both pheromone dispensing systems decreased moth catch to similar levels at 5-10 m from the central release point, but there was 5.5-fold more pheromone released from aerosol cans than from polyethylene dispensers over a 24 h period. Trap catches were reduced by about 90% in plots treated with either five aerosol cans per hectare or uniform deployment of polyethylene dispensers. Recordings of electroantennograms in open grassed plots and orchards indicated that the treated cotton pad of an aerosol dispenser and a point source of 100 polyethylene tubing dispensers produced similar electroantennogram recordings. Electroantennogram recordings provided evidence that pheromone plume detection from a single-point source was maintained over a range of 5-40 m downwind in the orchard. On present evidence, aerosol pheromone dispensers could not be recommended for further testing towards control of E. postvittana under New Zealand conditions owing to their higher cost of purchase and operation.     

Computational fluid dynamics evaluation of the effect of different city designs on the wind environment of a downwind natural heritage site

Disturbance in wind regime and sand erosion deposition balance may lead to burial and eventual vanishing of a site.This study conducted 3D computational fluid dynamics(CFD)simulations to evaluate the effect of a proposed city design on the wind environment of the Crescent Spring,a downwind natural heritage site located in Dunhuang,Northwestern China.Satellite terrain data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer(ASTER)Digital Elevation Model(DEM)were used to construct the solid surface model.Steady-state Reynolds Averaged Navier-Stokes equations(RANS)with shear stress transport(SST)k-ωturbulence model were then applied to solve the flow field problems.Land-use changes were modeled implicitly by dividing the underlying surface into different areas and by applying corresponding aerodynamic roughness lengths.Simulations were performed by using cases with different city areas and building heights.Results show that the selected model could capture the surface roughness changes and could adjust wind profile over a large area.Wind profiles varied over the greenfield to the north and over the Gobi land to the east of the spring.Therefore,different wind speed reduction effects were observed from various city construction scenarios.The current city design would lead to about 2 m/s of wind speed reduction at the downwind city edge and about 1 m/s of wind speed reduction at the north of the spring at 35-m height.Reducing the city height in the north greenfield area could efficiently eliminate the negative effects of wind spee.By contrast,restricting the city area worked better in the eastern Gobi area compared with other parts of the study area.Wind speed reduction in areas near the spring could be limited to 0.1 m/s by combining these two abatement strategies.The CFD method could be applied to simulate the wind environment affected by other land-use changes over a large terrain.     

The Performance of Rotating Metal-Foam Atomisers1

Prototype rotating metal-foam atomisers, designed for aerial application, have been extensively tested both in the laboratory and under field conditions. Laboratory tests were carried out in a wind tunnel and field tests in a large-scale aerial operation. The metal-foam atomisers showed advantages in droplet-spectrum control and vibration levels over currently available equipment, and, when used to spray 150,000 ha of cotton, four units required no maintenance. Rotating metal foam atomisers can operate safely at the high rotational speeds used for medium volume spraying of droplets with a diameter less than 50 μm (as in tse-tse control).     

Comparison of collectors of airborne spray drift. Experiments in a wind tunnel and field measurements

BACKGROUND: In this study, the collecting efficiency of different samplers of airborne drift was compared both in wind tunnel and in field experiments. The aim was to select an appropriate sampler for collecting airborne spray drift under field conditions. RESULTS: The wind tunnel study examined three static samplers and one dynamic sampler. The dynamic sampler had the highest overall collecting efficiency. Among the static samplers, the pipe cleaner collector had the highest efficiency. These two samplers were selected for evaluation in the subsequent field study. Results from 29 individual field experiments showed that the pipe cleaner collector on average had a 10% lower collecting efficiency than the dynamic sampler. However, the deposits on the pipe cleaners generally were highest at the 0.5 m level, and for the dynamic sampler at the 1 m level. CONCLUSIONS: It was concluded from the wind tunnel part of the study that the amount of drift collected on the static collectors had a more strongly positive correlation with increasing wind speed compared with the dynamic sampler. In the field study, the difference in efficiency between the two types of collector was fairly small. As the difference in collecting efficiency between the different types of sampler was small, the dynamic sampler was selected for further measurements of airborne drift under field conditions owing to its more well‐defined collecting area. This study of collecting efficiency of airborne spray drift of static and dynamic samplers under field conditions contributes to increasing knowledge in this field of research. Copyright © 2011 Society of Chemical Industry     

Quantitative studies on dispersal of Pseudocercosporella herpotrichoides spores from infected wheat straw by simulated rain

Splash dispersal ofPseudocercosporella herpotrichoides spores from infected wheat straw was investigated using simulated rainfall (rate 13.8l h^–1 m^–2, volume mean diameter 2.9 mm) and wind (2 m sec^–1) in a raintower/wind tunnel complex. Spores were deposited on the floor of the wind tunnel up to 1 m upwind and 2.5 m downwind from the centre of the straw and impacted on vertical surfaces at heights up to 36 cm above it. Fewer spores were collected with increasing distance from the straw and with increasing height. Most spore-carrying splash droplets were in the size range 400–600 m and very few were less than 200 m.Our results show that these spores are generally dispersed over short distance, which is consistent with field observations.Samenvatting Spetterverspreiding vanPseudocercosporella herpotrichoides van besmet tarwestro werd onderzocht met behulp van nagebootste regen (13,8 l uur^–1 m^–2, gemiddelde druppel diameter 2,9 mm) en wind (snelheid 2 m sec^–1) in een proefopstelling van een regentoren en een windtunnel. Sporen werden op de vloer van de windtunnel gedeponeerd tot 1 m afstand tegen de wind in, gerekend vanaf het centrum van het tarwestro, en met de wind mee tot 2,5 m afstand daarvan. Op verticale vlakken werden sporen op een hoogte van 0 tot 36 cm boven de vloer van de windtunnel opgevangen. Naarmate de afstand en de hoogte toenamen werden er minder sporen gevonden. De meeste spetters met sporen hadden een diameter van 400–600 m en slechts enkele waren kleiner dan 200 m.Onze resultaten tonen aan dat de sporen in het algemeen slechts over korte afstanden verspreid worden, hetgeen overeenkomt met veldwaarnemingen.     

Head Blight Gradients Caused by Gibberella zeae from Area Sources of Inoculum in Wheat Field Plots

ABSTRACT The spread of Fusarium head blight of wheat from a small area inoculum source was examined in wheat plots (100, 625, or 2,500 m(2)) inoculated in the center with Gibberella zeae-colonized corn kernels or macro-conidia sprayed on heads at anthesis. With the first inoculation method, disease foci were produced from ascospores released from perithecia formed on inoculated kernels. With the second inoculation method, disease foci were produced by macroconidia directly applied to the heads. Some plots were misted during anthesis. Plots were divided into grids, and disease incidence on spikelets and seeds was assessed at the grid intersections. Isopath contour maps were constructed using an interpolation procedure based on a weighted least squares method. Disease gradients were constructed from the isopath contours in the direction parallel to average nightly wind vectors using an exponential model. This study was conducted over a 3-year period at two sites: one in Quebec and one in Ontario. Both inoculation methods resulted in a discrete, primary focus of head blight in each plot, with one or two smaller secondary foci in some plots. The highest incidence of disease on spikelets or seed was commonly displaced somewhat from the inoculum source, usually downwind. The gradient slopes of seed and spikelet infection ranged from -0.10 to -0.43 m(1) in plots with ascospore inoculum and from -0.48 to -0.79 m(1) in plots inoculated with macroconidia. Seed infection declined to 10% of the maximum within 5 to 22 m from the focal center in asco-spore-inoculated plots, and within 5 m in a macroconidia-inoculated plot. Gradients were usually steeper upwind compared with downwind of the inoculum source. In misted plots, incidence of disease was higher and more diffuse than in nonirrigated plots. Based on gradients and dispersal patterns, disease foci in plots inoculated with G. zeae-colonized corn kernels probably arose from airborne ascospores rather than from splash-borne macroconidia and were the result of infection events that occurred over a short period of time. Comparison of conidial- and ascospore-derived disease gradients indicated a lack of secondary infection, confirming that Fusarium head blight is primarily a monocyclic disease.     

格状沙障内风速波动特征初步研究

通过对不同孔隙度格状沙障内风沙流中风速波动特征研究发现:风沙流中各高度层风速波动具有很好的相关性,其波动幅度随孔隙度的增加而减小;瞬时风速在时间序列上波动的均一性随不同高度间距离增加呈递减趋势;瞬时风速的波动性一方面受下垫面性质及外在环境条件的影响,另一方面与其所在高度层沙粒数量和运动状态有关.     

Effects of sand-fixing and windbreak forests on wind flow: a synthesis of results from field experiments and numerical simulations

Sand-fixing and windbreak forests are widely used to protect or/and improve the ecological environments in arid and semi-arid regions. A full understanding of wind flow characteristics is essential to arranging the patterns of these protective forests for enhancing the effectiveness. In this study, the wind velocity over the underlying surface with sand-fixing forests and windbreak forests at the heights of 1–49 m was monitored from two 50-m high observation towers in an oasis of Minqin, Gansu Province of China. The wind velocities were simulated at different locations over these protective forests between those two towers by a two-dimensional Computational Fluid Dynamics(CFD) model. The results showed that at the heights of 1–49 m, the wind velocity profiles followed a classical logarithm law at the edge of the oasis and a multilayer structure inside the oasis. With increasing number of sand-fixing forest and windbreak forest arrays, the wind velocity at the heights of 1–49 m generally decreased along the downstream direction of the prevailing wind. Specifically, below the height of windbreak forests, the wind velocity decelerates as the airflow approaches to the windbreak forests and then accelerates as the airflow passes over the windbreak forests. In contrast, above the height of windbreak forests, the wind velocity accelerates as the airflow approaches to the windbreak forests and then generally decelerates as the airflow passes over the windbreak forests. Both the array number and array spacing of sand-fixing and windbreak forests could influence the wind velocity. The wind protection effects of sand-fixing forests were closely related to the array spacing of windbreak forests and increased with the addition of sand-fixing forests when the array of the forests was adequately spaced. However, if the array spacing of windbreak forests was smaller than seven times of the heights of windbreak forests, the effects were reduced or completely masked by the effects of windbreak forests. The results could offer theoretical guidelines on how to systematically arrange the patterns of sand-fixing and windbreak forests for preventing wind erosion in the most convenient and the cheapest ways.     

Spray impaction,retention and adhesion: An introduction to basic characteristics

Droplets, falling under gravity through air that is not moving relative to the target, will impact on any object in their path, while charged droplets will be drawn to objects of earth potential along paths normal to the lines of equipotential; thus near the catching surface, they will move directly towards it. If the air is moving relative to the target, it will tend to move the droplets with it. The greater the drag to mass ratio of a droplet, the more rapidly any initial motion it has through the air will cease, and it will move through the air only very slowly under the effects of gravity and any electromagnetic potential. Air flowing past an object is able to change its path rapidly, but droplets moving with the air are less able to do this. Their ability to avoid impact increases with decrease in droplet size and wind speed, and with increase in the size of the catching surface. Thus small smooth stems catch big droplets in a high wind efficiently, but large smooth branches in a light wind will not catch many small droplets. Artificial cylinders and ribbons are poorer at catching droplets than natural surfaces, which are rarely smooth and often hairy. Hairs or spikes on a surface greatly increase the catch efficiency of droplets carried in the wind. A droplet several hundred micrometres in diameter is so dominated by gravity that it will fall in a near vertical path even in a moderate wind, impacting on any horizontal surface that obstructs its path. Its chances of reaching a vertical stem are negligible unless it runs off or splashes from a near horizontal surface. Conversely, a small droplet will be carried almost horizontally in any wind and is most likely to impact on vertical surfaces or flapping leaves. It has a much greater chance of getting inside the canopy without being caught because most leaves are near horizontal, and once there, it must rely on the turbulence induced by the wind for transport and impaction on undersurfaces or hairs. Because turbulence is reduced as the droplet nears the ground, it is very difficult to catch droplets on the lower parts of the crop within the canopy. To bounce, a droplet must have enough surplus kinetic energy to rebound clear of the surface, allowing for the energy losses in deforming the droplet in the bounce process; moreover, the surface must not be significantly wetted by the drop. Thus the droplet must be moderate to large in size, must be moving rapidly relative to the surface, and must have a high surface tension to contain it as a droplet, even at its extreme deformation. Surface condition is of great importance; the presence of hairs and the type of roughness affect the probability of maintaining an air film between the surface and the droplet. In general, droplets below 150 μm diameter are unlikely to bounce, but adding small amounts of surfactant to the droplet formulation can increase this size by several times. Any one plant leaf can vary considerably over its area because of age, abrasion and local surface shape. A film of water on a wet surface ensures an air film is maintained and the droplet will bounce.     

Comparison of wind tunnel and field experiments to measure potential deposition of fenpropimorph following volatilisation from treated crops

The potential for short-range transport via air, i.e. volatilisation from the area of application and subsequent deposition on adjacent non-target areas, was investigated for the fungicide fenpropimorph in a wind tunnel system and under outdoor conditions in a higher-tier field study. Fenpropimorph 750 g L(-1) EC was applied post-emergence to cereal along with a reference standard lindane EC. Stainless steel containers of water were placed at different distances downwind of the application area to trap volatile residues during a study period of 24 h following application. Meteorological conditions in the wind tunnel as well as on the field were constantly monitored during the study period. The wind tunnel system was a partly standardised system on a semi-field scale, i.e. wind direction and wind speed (2 m s(-1)) were constant, but temperature and humidity varied according to the conditions outside. In the field experiment, the average wind speed over the 24 h study period was 3 m s(-1) and no rainfall occurred. Three different measuring lines were installed on the non-target area beside the treated field to cover potential variations in the wind direction. However, no significant differences were observed since the wind direction was generally constant. Fenpropimorph was detected in minor amounts of 0.01-0.05% of the applied material in the wind tunnel experiment. Even at a distance of 1 m beside the treated field, no significant deposition occurred (0.04% of applied material after 24 h). In the field, less than 0.1% of the applied fenpropimorph was detected at 0 m directly beside the treated field. At 5 m distance the deposition values were below 0.04%, and at 20 m distance about 0.01%. In general, the amounts of deposited fenpropimorph detected in the partly standardised wind tunnel system and the higher-tier field study were in good agreement.     

Spray deposit patterns and persistence of diflubenzuron in some terrestrial components of a forest ecosystem after application at three volume rates under field and laboratory conditions

Spray deposit patterns and persistence of diflubenzuron [1-(4-chlorophenyl)- 3-(2,6-difluorobenzoyl)urea] in white pine (Pinus strobus L.) and sugar maple (Acer saccharum Marsh.) canopies, forest litter and soil were studied after aerial application of a 250 g kg^?1 wettable powder formulation, ‘Dimilin® WP-25’, at 70 g active ingredient (a.i.) ha^?1, using three volume rates (10, 5 and 2.5 liters ha^?1) over three blocks in a mixed forest near Kaladar, Ontario, Canada, during 1986. Spray droplets were sampled at ground level using ‘Kromekote®’ cards, and diflubenzuron deposits were collected on glass plates. Droplets were the largest (with a volume median diameter of 250 μm) at the 10 liters ha^?1 rate, resulting in the highest number of droplets per cm² on the Kromekote cards and deposits of diflubenzuron on glass plates. Deposits on foliage, litter and soil were also correspondingly the highest. At the 5.0 and 2.5 liters ha^?1 rates, volume median diameter values were smaller (195 and 150 μm, respectively) and deposits on the substrates were markedly lower. In the spray block that received 10 liters ha^?1, diflubenzuron persisted in foliage as long as 120 days after treatment, but it lasted for only about a week in forest litter and soil samples. At 5 and 2.5 liters ha^?1, diflubenzuron failed to persist in foliage as long, and residues in litter and soil, which were barely above the quantification limit, persisted only for a few days. Laboratory studies, conducted under constant meteorological conditions using different droplet-size spectra, showed that deposit levels were not affected when the volume median diameter of the spray cloud decreased from 253 μm to 145 μm, but were markedly reduced as this progressively decreased from 92 to 37μm. The dissimilarities between the field and laboratory findings were attributed to meteorological and other factors influencing droplet deposition on tree canopy in aerial applications of pesticides over forests.