Effects of formulation on spray nozzle performance for applications from ground-based boom sprayers

The performance of agricultural spray nozzles has components relating to the droplet size and velocity distributions within the spray, spray structure, entrained air characteristics and the spray volume distribution pattern. The interaction of these physical performance parameters has been shown to influence target retention, efficacy and the risk of drift. Results from a number of studies have also shown that the physical properties of the spray liquid have a substantial effect on spray formation such that changes in formulation type can give changes in spray characteristics that would be equivalent to doubling the flow rate through conventional hydraulic flat fan nozzles. The interactions between the physical properties of the spray liquid and the characteristics of the spray formed is a function of nozzle design. However, analysis of a large data set for a range of types of hydraulic pressure nozzle has shown that sprays formed from liquids based on emulsions generally have a coarser droplet size distribution compared with sprays formed from surfactant solutions. Although some correlation between dynamic surface tension and viscosity with spray droplet size has been established, the results from work reviewed in this paper suggest that other factors also influence the spray formation process. Air induction and twin-fluid nozzles mix air and liquid in the spray formulation process to produce droplets with air inclusions. These nozzle designs have been found to have a performance that is more sensitive to changes in spray liquid properties compared with hydraulic pressure nozzles and to exhibit trends that are different from those of conventional nozzle types.     

A comparison of initial spray characteristics produced by agricultural nozzles

Pesticides are commonly applied by using hydraulic nozzles to generate droplets. The properties of these spray droplets can influence the effectiveness and risks associated with the use of pesticides. Initial spray characteristics (initial droplet size and velocity, fan angle and spray liquid density) were therefore measured for a range of hydraulic nozzles and spray mixtures. Particle Image Velocimetry (PIV) was used to measure the spray sheet velocity.There was a significant difference between a standard hydraulic nozzle, Turbo TeeJet^® and air induction nozzle for all measured spray characteristics. The standard hydraulic nozzle generated the smallest droplet sizes, the highest velocity and the highest spray liquid density. The air induction nozzle generated the largest droplet size, the slowest velocity and the lowest spray liquid density. The type of air induction nozzle and spray formulation was also found to influence spray characteristics.This work has demonstrated that initial spray characteristics such as droplet size and velocity, liquid density, fan angle and included air can vary depending on nozzle design, operating parameters and spray formulations. Initial droplet velocity was found to be significantly correlated to droplet size (D_v0.5) and spray pressure.     

Spray drift review: The extent to which a formulation can contribute to spray drift reduction

Mitigation of risk arising from spray drift in Europe is achieved mostly by implementation of no-spray buffer zones and the use of approved drift-reducing techniques. Although physicochemical properties of spray solutions are known to influence spray drift, they are not yet incorporated into regulatory risk assessments at the European level. In this review we give a systematic report on the relevant physical properties of agricultural spray liquids and how these influence spray characteristics. According to the data reported in literature, it can be concluded that not only spray-mix additives but also certain formulation types can be used to reduce spray drift. To complete the picture, existing drift mitigation techniques and conditions have been reviewed along with measuring equipment which is commonly used to characterize agricultural sprays and the droplet size-related biological aspects of the application process. In a final step, we discuss the possibility of estimating drift risk based on the physicochemical properties of spray liquids induced by different formulation types.     

Assessing the deposition and canopy penetration of nozzles with different spray qualities in an oat (Avena sativa L.) canopy

Consistent spray coverage that is evenly distributed throughout the canopy is necessary to control pest populations that can negatively affect yield. As applicators are switching to Coarser spray quality nozzles to reduce risk and liability of pesticide spray drift, concerns about efficacy loss are growing. Previous research has indicated that small droplets are the most effective at penetrating through crop canopies, but newer nozzle technologies have improved the effectiveness of larger droplet or Coarser sprays. Research was conducted to assess the canopy penetration of nozzles that produce Coarse, Very-Coarse and Extremely-Coarse spray qualities compared to nozzles that produce Fine and Medium spray qualities. Kromekote collectors were positioned in four configurations in an oat (Avena sativa L.) var. ‘Yarran’ (AusWest Seeds, Forbes, NSW, Australia) crop to quantify the coverage and droplet number densities (droplets cm⁻²) across three application carrier volume rates: 50, 75 and 100 L ha⁻¹. Applications were made in the field in 30 cm tall, tillering oats, with collectors arranged in a randomised complete block design with three replications. The entire study was repeated on the following day. Results showed that droplet number densities were inversely related to the droplet size produced by the nozzles, yet coverage was increased more by application volume rate than droplet size. Thus, both spray drift reduction and improved canopy penetration can be achieved with proper nozzle selection and operation parameters for the control of agronomic pests.     

Characteristics and classification of Japanese nozzles based on relative spray drift potential

European spray nozzle drift classifications have enabled the objective evaluation of the drift reduction performance of different nozzles with various operating parameters available in certain areas. The drift potential index reduction percentage (DIXRP) for one series of drift reduction nozzles used in Japan was investigated by wind tunnel tests. Based on the reference spray (Hypro ISO F110 03), most of the YAMAHO KIRINASHI ES nozzles had DIXRP values above 50% at nozzle heights from 0.3 m to 0.5 m, which means these nozzles can be considered as drift reduction nozzles. The best nozzle height range was found to be between 0.3 m and 0.4 m above the crop canopy. In addition, the DIXRP values were above 80% for a nozzle height of 0.3 m, except for one nozzle (the ES 05) which had the smallest droplet size and low flow rate which contributed to the large decrease in the DIXRP values when nozzle pressure increased. Large droplet diameter, high droplet velocity and low recommended nozzle height are considered to be important factors that can provide good drift reduction performance although droplet velocity was not measured in this study. The DIXRP value was inversely proportional to nozzle height. In addition, the influence of nozzle size on the DIXRP values was found to be statistically significant (P < 0.01), although the influence was not as obvious as that of nozzle height. Finally, a nozzle classification system for use in Japan based on the relative drift potential has been established.     

A meta analysis of spray drift sampling

There are many methods available for sampling spray drift, and a great variety of estimates of spray drift have been published. Available data on spray drift were collected from different studies and the measurements of spray drift were analysed to determine similarities and differences between the individual studies. Each of the methods varied significantly in their estimates of spray drift. This variation was due to many factors that differed between the published sources, such as environmental conditions, cropping system, equipment used and the tracer used. It is suggested that in order to compare drift measurements between published studies, measurement techniques and sampling distances must be standardised, and environmental conditions (humidity and temperature) should be restricted to within certain boundaries in the field, and controlled within artificial tests, unless, of course, the effect of this variable on drift is being examined.     

Spray drift: impact of requirements to protect the environment

Spray drift studies in the US have evaluated the effects of application, meteorological and tank mix variables on spray drift. The data have been incorporated into models to predict drift from aerial applications, and to evaluate worst-case drift from ground rig (boom) and orchard airblast applications. An atomisation model has also been developed to predict droplet size for applications of tank mixes with user-defined or reasonable worst-case physical properties through a wide range of hydraulic nozzles applicable to aerial applications. The database and models help provide the exposure risk input to risk assessments for developing appropriate labelling based on exposure and toxicity risk to non-target sensitive areas. This needs to be balanced with allowing crop protection using careful risk/benefit assessments. Buffers or no spray zones may be based on spray quality, release height and other variables such as wind speed where necessary for protecting specific sensitive areas. The impact of protection measures aimed at minimising the incidence and impact of spray drift is discussed in the present paper.     

Distribution patterns of aerially applied ULV sprays by aircraft over and within the cotton canopy in the Sudan Gezira

A series of experimental ULV sprays by aircraft were conducted over four 35 ha cotton fields in the Sudan Gezira. The aim was to compare the pattern of deposit distribution over and within the cotton canopy when two ULV spray spectra designated for convenience as coarse (120 μm VMD) and fine (80 μm VMD) were released in the early morning (0600 h), mid-morning (0900 h), midday (1130 h) and mid-afternoon (1530 h). Results showed that early morning sprays produced a rather narrow useful swath from both coarse and fine sprays and high risk of drift from fine droplets. Both droplet spectra in the mid-morning spray, on the other hand, provided a good deposit pattern within the cotton canopy and had the least amount in the air at 100 m downwind. Furthermore, the fine spray gave a swath almost 50% wider than the coarse one. At noon the swaths were approximately intermediate to those of the early and mid-morning sprays. However, the variation of deposits at any one point was large and the amounts remaining airborne at 100m downwind were substantial. During mid-afternoon, wind over the Gezira was generally light and variable. As, in practice, the pilot flies invariably along the length of the field rather than across the wind direction, mid-afternoon sprays produced peaky deposits over a narrow swath. With regard to penetration of spray droplets into the canopy, the physical structure of the latter proved to be the determining factor. Turbulence generated by wind or the aircraft had no detectable effect.     

Atomizers for the aerial application of herbicides—ideal and available

Reduction of spray drift is essential when herbicide sprays are applied from aircraft: sprays with a narrow spectrum and a droplet volume median diameter of about 225 μm are therefore required. Analysis of the performance of atomizers currently available suggests that one of the best is a flat fan hydraulic nozzle (8005) set at 45 degrees downwards and backwards relative to the flight direction. About 33% of the volume emitted by this atomizer is within 25% of this desired size. A new windmill disc atomizer, 50 mm in diameter, produces 70% of the volume emitted in this size range with less than 5% in droplets smaller than 150 μm. This is achieved by having far greater control over the actual atomizing condition, ensuring ligament formation even at flow rates approaching one litre per minute. A strong radial airflow at the atomizing edges is extremely beneficial.     

Effects of charging voltage,application speed,target height,and orientation upon charged spray deposition on leaf abaxial and adaxial surfaces

Wastage of agricultural chemicals and ensuing environmental pollution is an issue, where ineffective spray deposition is a major concern with conventional pesticide application methods. Electrostatic spraying is known to be one of the most effective methods to improve leaf abaxial (underside) surface deposition, overall deposition, and distribution on the plant targets. Deposition of charged sprays on leaf abaxial and adaxial (upper) surfaces as influenced by the spray charging voltage (system), application speed (operational), target height and orientation (target) parameters was studied in the laboratory. An air-assisted electrostatic induction spray charging system attached to a moving carriage was used to apply charged spray at uniform application (ground) speeds. Spray deposition (101–71 μm NMD), determined using a fluorescent tracer technique increased with charging (0–5.5 mC kg⁻¹) on leaf abaxial and decreased with charging on adaxial surface. The deposition was higher on abaxial (0.66–1.33 μg cm⁻²) at 30° below (horizontal plane) and on adaxial (0.78–1.79 μg cm⁻²) at 0° (horizontal) target orientation for lower (0.278 m s⁻¹) application speed. At all target heights, abaxial deposition increased with charging voltage (0–4.0 kV) for medium application speed (0.417 m s⁻¹) and adaxial deposition decreased with charging voltage for lower application speed (0.278 m s⁻¹). The medium application speed with higher charging voltage was optimum for abaxial and adaxial deposition. The droplet velocity and charging voltage were the key factors for obtaining desired spray deposition on targets. All the selected factors including target orientation (O), application speed (S), target surface (L), and charging voltage (V), and their interactions except between O and S were significant at lower (0.35 m) and medium (0.65 m) target heights. All the factors and their interactions except between O and V were significant at higher (0.95 m) height. Electrostatically charged spray improved the underside (abaxial) and overall deposition. The deposition was substantially influenced by factors such as charging voltage, application speed, plant target height, and target orientation.     

Effects of spray adjuvants on swath patterns and droplet spectra for a flat-fan hydraulic nozzle

The effects of seven agricultural adjuvants and two polymeric drift retardants on the distribution of spray were compared with water applied through a multiple nozzle boom. Similarly, the effects on droplet spectra from a single XR80004VS nozzle operating at 276 kPa (40 p.s.i.) were compared. Except for two adjuvants, swath pattern relative to water was significantly altered. With one exception, droplet spectra parameters relative to water were shifted to both smaller and larger frequency distributions. The polymers, whether sprayed alone or in mixture, had the greatest effect on swath pattern. The polymers sprayed alone had the greatest effect on droplet spectra, but the mixtures gave a more variable response. Swath patterns and droplet spectra derived using water are not, therefore, representative when spraying pesticides with adjuvants. Dynamic surface tension (DST) and viscosity at high shear rates were measured for all spray solutions. Analysis to determine the feasibility of predicting quality of swath pattern and various spray spectra parameters (e.g. VMD, NMD) showed that the interaction between the two physicochemical parameters and the results of atomization are complex. DST and viscosity were poor predictors when applied to the mixtures of polymers and conventional adjuvants tested.     

Deposition of spray drift behind border structures

Windbreaks present a porous obstacle to the approaching airflow, forcing air to flow through the windbreak at a reduced speed and accelerate over the top. In this research, windbreaks were considered as border structures to mitigate spray drift. Air flows, with an interspace between it, particles are filtered from the flow by deposition on the windbreak. Hence there is a reduction in deposition in the downwind sheltered area (the ‘quiet zone’) behind the windbreak. Peak deposition in the sheltered area can occur at minimum wind speeds. The deposition profiles of spray drift behind various border structures were measured. In the first part, drift tests were performed in a wind tunnel. Artificial screens with various heights and open areas were tested. A row of plastic Christmas trees and natural canopies were also tested. Subsequently, drift experiments were performed under field conditions in a grassland with the artificial screens and a row of Fagus sylvatica trees. The artificial screens reduced spray drift deposition in the sheltered region, but significant deposition peaks were found behind the screens. The natural structures had potential to reduce drift deposition when their height was at least equal to the height of the spray nozzle(s). The drift deposition at short distances behind the natural structures was higher than deposition behind artificial structures, but conversely peaks in deposition in sheltered areas were not created by the natural structures.     

Assessment of spray drift in sloping vineyards

The phenomenon of spray drift in the context of spray application is discussed, and some results of experimental measurements of drift during treatments of sloping vineyards are presented. The various factors causing drift are explained and evaluated. Five main factors (application method, droplet-size spectrum, wind speed, special-risk areas, and characteristics of the chemical(s)) are most important. A matrix pattern for estimating drift hazards is proposed as a means of assessing whether a spray can be applied without drift exceeding a certain ‘tolerable’ level.     

Pressure,droplet size classification,and nozzle arrangement effects on coverage and droplet number density using air-inclusion dual fan nozzles for pesticide applications

Spray applications are most effective when they cover the greatest per unit area, improving target pest control. In order to optimize spray applications, nozzle companies have developed new designs that seek to provide the greatest and most uniform coverage per target unit area. While dual fan nozzles have been examined against single fan nozzles in several studies, there has not been a comprehensive comparison of multiple nominal flow rate and multiple dual fan nozzle types. This study sought to examine pressure, droplet size classification, and nozzle arrangement effects on droplet number density on horizontal artificial collectors using a fixed application rate. The relationship between coverage and nozzle type was significant (P < 0.001) as was the relationship between coverage and pressure (P < 0.001). The 207 kPa pressure resulted in the highest coverage for every nozzle type except the alternating TADFs (ATADF)s. The GAT 11003 resulted in the highest coverage overall with 39.6% at the 207 kPa pressure, followed by the TADF 11005 and TADF 11003 at 38.6% and 38.3% coverage respectively. The effect of pressure was significant for the droplet number density (P < 0.001) as was the effect on droplet number density from nozzle type (P < 0.001). The 414 kPa pressure resulted in the highest droplet number density for all nozzle types except the AITTJ 11003 and the MDD 11004. The GAT 11003 and GAT 11004 produced the highest overall droplet number densities with 73.0 and 72.6 droplets cm² at the 414 kPa pressure. The GAT 11003 had the greatest droplet number density at every pressure. Nozzle arrangement has a significant effect on spray coverage with asymmetric dual fan nozzles, and it would be recommended to alternate these nozzles on a spray boom to increase coverage especially at higher application speeds. Results from this study show that an applicator can select a coarser droplet size classification without observable loss in coverage, while greatly reducing the drift potential of the application.     

New developments in pesticide-application technology

Greater awareness of the inefficiency of pesticide application, water-supply problems, the need for more rapid and timely treatment, and the increased cost of pesticides, have stimulated development of new application techniques. Changes in nozzle design can produce sprays with a narrower droplet spectrum; the introduction of electrostatically charged sprays provides greater control of droplet trajectories to increase deposition and reduce downwind drift. Improvements in hand-carried, vehicular and aerial spraying are briefly reviewed, together with granule application and seed treatment. Introduction of closed systems to transfer pesticides from containers to the spraying equipment is expected to reduce operator contamination; this will be combined with a trend towards spray equipment with microprocessor controls, and further development of pesticide formulations.     

Physical,chemical and biological appraisal of alternative spray techniques in cereals

In a multidisciplinary study, spinning disc, rotary cage, electrostatic aqueous and electrodynamic methods of atomization were compared with conventional systems based on various types of flat-fan hydraulic-pressure nozzles commonly used in farm practice. The 80-degree type hydraulic nozzles at 200 l/ha rate produced the largest proportion of droples greater than 350 μm whereas the 110-degree type at the same rate produced the largest quantity of droplets below 50 μm. The effects of electrostatic charging on droplet spectra of aqueous sprays was slight at 200 l/ha rate but at 70 l/ha the proportion by volume of both the largest and smallest droplets was significantly reduced. The rotary cage atomizers produced a droplet spectrum of intermediate width whereas the spinning disc and electrodynamic systems yielded the narrowest spectra. In terms of tracer deposition, the hydraulic nozzles (especially the 110-degree type) used at about 200 l/ha produced the most even partitioning of spray within the crop and yielded the lowest coefficients of variation (CV) of mean deposits both on cereal plant parts and on weeds. The rotary cage, spinning disc and ‘Electrodyn’ either yielded high CV values or lacked penetration into the crop structure. In barley at an early growth stage (GS 31), there was little effect on tracer deposition by electrostatic charging of aqueous sprays, whereas at GS 57 charging at the 70 l/ha rate increased deposition in the upper plant parts. The hydraulic nozzle systems (especially the 110-degree type) were generally the most effective for weed and disease control and produced the highest grain yields from fungicide applications. All methods of spraying, however, produced a significant yield gain from fungicide applications.     

Comparative performance of recycling tunnel and conventional sprayers using standard and drift-mitigating nozzles in dwarf apple orchards

The use of tunnel sprayers should be encouraged because they can potentially reduce pesticide input and drift in orchards. They could also allow smaller plot size in multifactorial trials in which fully randomized or randomized block designs are recommended. However, the effectiveness of plant protection products applied with tunnel sprayers cannot be reliably assessed without a thorough investigation into spray distribution in tree canopies. A set of three experiments was undertaken in an apple orchard to compare a new type of recycling tunnel sprayer with a standard axial fan sprayer, both of them fitted with either conventional hydraulic hollow cone nozzles (ATR) or drift-mitigating air induction cone nozzles (TVI). Its performance was assessed in terms of 1) spray deposit and coverage in the canopy, 2) sedimentation drift (spray drift to the ground) and 3) collection and recycling rate of the liquid sprayed in the tunnel. Artificial targets composed of cellulose papers and water-sensitive papers were used to evaluate the spray deposit and coverage at similar target positions for each treatment. A fluorescent dye was used as the spray tracer.     

Volumetric validation of mass balance using a computational phase Doppler approach for disc core nozzles

The mass balance of orchard air-blast sprayers has historically been assessed using an array of samplers to capture airborne particles. However, these methods only provide an idea of flux with no other information which is pertinent to understand the movement of droplets and their potential to drift. While droplet analysis for agricultural sprayers has always been conducted in a laboratory setting with the use of laser devices, a new phase Doppler approach is being explored to assess droplet spectra, velocity, and flux in outdoor field conditions. Therefore it is the objective of this study to develop a methodology and the potential limitations for using a phase Doppler system while in a laboratory setting. Due to the expected variability of field conditions as well as the turbulence of orchard sprayers, a computational approach was sought to assess flux from a single scan of a conical spray plume's diameter. Using a constant scanning speed of 0.0079 m/s, a disc core (D1/DC33) hollow cone nozzle was examined at 310, 410, and 520 kPa pressure at five different heights (10, 20, 30, 40, and 50 cm). Computational flux was then compared to the actual flow rate, finding a −3.3% average error with a range of −16.9% and 4.7% illustrating a small underestimation of mass with the phase Doppler which was related to distance and droplet frequency. Further, comparisons were also assessed including pattern/symmetry, droplet spectra, velocity, and the overall number of samples. The proposed methodology indicates potential for the use of phase Doppler technology for in situ measurements of spray equipment using a conical-type spray nozzle, such as that of the orchard air-blast sprayer.     

Effects of application methods,spray volumes,pressures and herbicide rates on weed control in spring cereals

Herbicides were sprayed in spring cereals with conventional and low pressure hydraulic flat-fan spray nozzles and rotary atomizers. The biological effects were measured on weeds and oats. In addition, some spray retention studies were performed. Conventional flat-fan spray nozzles at a spraying pressure of 2 or 4 bar (200 or 400 kPa) gave the best effect. There was no difference in effect between spray volumes of 125 1/ha and 250 1/ha. In most field situations, 200 kPa and 125 1/ha should be preferred. However, when the spray volume is reduced from 250 to 125 1/ha, the droplet size decreases and the drift hazard increases. Where great care has to be taken, the use of conventional flat-fan spray or low-pressure nozzles at 100 kPa and 250 1/ha may be a compromise between effect and safety.