Air-assisted Sprayer Research Articles

Spray volume deposits and fungicide efficacy on soybean rust (Phakopsora pachyrhizi)

Soybean rust (SBR), caused by Phakopsora pachyrhizi, is one of the most destructive fungal diseases affecting soybean yields in many countries. Fungicide application methods that provide better SBR control efficacy may reduce soybean losses due to this disease. We investigated the effects of spray volumes applying the fungicide pyraclostrobin plus epoxiconazol at 133 + 50 g a.i. ha-1 by a conventional sprayer (CS) and an air-assisted sprayer (AAS). Field experiments were conducted comparing the effects of spray volumes of 110, 160, and 210 L ha-1 and two application techniques (CS and AAS) on spray deposits and SBR control. Fungicide efficacies were measured by disease severity, thousand seed weight, and yield. Correlations between disease severity and yield were also assessed. All treatments were applied with an Advance 2000 AM18 sprayer. In general, SBR disease and yield did not differ significantly when fungicide applications were applied with AAS compared to CS. Increasing the spray volume from 110 to 210 L ha-1 did not increase spray deposit coverage on soybean leaves. Low disease severity was obtained by fungicide applications using a spray volume of 210 L ha-1. Safe recommendations of ground spray volumes for SBR control should be between 160 and 210 L ha-1, using hydraulic nozzles.

The smart spray analytical system: Developing understanding of output air-assist and spray patterns from orchard sprayers

Efficient chemical application is a critical operation during specialty crop production that requires constant sprayer calibrations as well as pertinent adjustments to avoid off target spray losses. However, lack of rapid and in-field assessment tools limit the opportunities for frequent adjustments of orchard sprayer attributes. To overcome such limitations, our team has developed a smart spray analytical system (SSAS). Using SSAS, this study evaluated two commercial orchard sprayers, S1 (Powerblast 400, Rears Manufacturing Co., Eugene, OR, USA) and S2 (Turbo-Mist S30P300NSHD, Slimline Manufacturing Ltd., Penticton, BC, Canada), for their air-assist velocity and spray delivery patterns. Air-assist velocity patterns were studied in controlled conditions along two major planes: along the sprayer air-outlet (P1) and parallel to an imaginary tree row wall (P2), representing specific distances from the sprayer to tree row middles. SSAS data aided in generating several 2-D contour plots of the air-assist velocities along both the planes and for both sides of selected sprayers. Spray delivery patterns were generated along the typical locations of tree row wall and were based on pertinent air-assist velocity patterns. Results suggested that the magnitude of air-assist velocities was higher on the right side for sprayer S1 and on left side for sprayer S2. Such differences could be attributed to the design of fans, blades, rotation, air-inlet and outlet. There existed a consistent shift in air-assist along P2 plane and hence the spray delivery pattern shift on either side of both the sprayers. The uniformity in air-assist velocities decreased with the increasing distance from sprayer outlet. Average symmetries of 82.02 ± 12.81 (standard deviation) % and 44.27 ± 11.44% were observed in air-assist patterns for sprayer S1 and S2 along the plane P1, respectively. Similarly, average symmetries of 87.67 ± 0.53% and 74.03 ± 1.56% were observed in spray delivery patterns for sprayer S1 and S2, respectively. Overall, SSAS was consistent in quantification of the air-assist velocities (standard error ≤ 0.45 m s−1) and spray delivery patterns (standard error ≤ 0.07 ml cm−2) of commercial orchard sprayers and can be used at manufacturing stage for building consistent units as well as in the orchard settings for adjusting sprayer attributes to achieve targeted delivery on to the crop canopies.

Control of Insects and Diseases with Intelligent Variable-rate Sprayers in Ornamental Nurseries

Abstract Intelligent spray technology can reduce pesticide use and safeguard the environment; however, its ability to effectively control insects and disease must be validated before its adoption by growers. Comparative tests for two different laser-guided variable-rate intelligent sprayers and the same sprayers with conventional constant-rate mode were conducted to control pests at two ornamental nurseries in two growing seasons in Ohio. Crabapple [Malus ‘Sutyzam’ (Sugar Tyme®), M. sargentii], apple (Malus pumila), maple [Acer ×freemanii ‘Jeffersred' (Autumn Blaze®), A. rubrum ‘Franksred' (Red Sunset®) and A. rubrum], birch (Betula nigra and Betula populifolia ‘Whitespire'), London planetree (Platanus ×acerifolia ‘Bloodgood') and dogwood (Cornus florida) were used as the test plants. Intelligent spray technology reduced pesticide use by 56.1% and 51.8% on average at the two nurseries, respectively. Compared to conventional air-assisted sprayers, severity of scab on apple trees and powdery mildew in dogwood was reduced on intelligent spray-treated plants at one nursery, and there were equal or fewer leafhoppers in maple trees and aphids in birch trees when sprayed using intelligent spray technology at both nurseries. These results suggest that intelligent, variable-rate sprayers achieve equivalent or greater insect and disease control in ornamental tree nurseries compared to conventional, constant-rate sprayers. Index words: aphid, apple scab, environmental protection, leafhopper, precision spray, powdery mildew, sustainable. Species used in this study: apple (Malus pumila Mill), birches (Betula nigra L, Betula populifolia Marsh. ‘Whitespire'), crabapples [Malus ‘Sutyzam' (Sugar Tyme®), M. sargentii Rehder], dogwood (Cornus florida L.), maples [Acer ×freemanii E. Murray ‘Jeffersred' (Autumn Blaze®), A. rubrum L. ‘Franksred'(Red Sunset®) and A. rubrum L.], London planetree [Platanus ×acerifolia (Ait.) Willd. ‘Bloodgood'].

Development and Field Evaluation of a Spray Drift Risk Assessment Tool for Vineyard Spraying Application

Spray drift is one of the most important causes of pollution from plant protection products and it puts the health of the environment, animals, and humans at risk. There is; thus, an urgent need to develop measures for its reduction. Among the factors that affect spray drift are the weather conditions during application of spraying. The objective of this study was to develop and evaluate a spray drift evaluation tool based on an existing model by TOPPS-Prowadis to improve the process of plant protection products’ application and to mitigate spray drift for specific meteorological conditions in Greece that are determined, based on weather forecast, by reassessing the limits for wind speed and direction, temperature, and air relative humidity set in the tool. The new limits were tested by conducting experimental work in the vineyard of the Agricultural University of Athens with a trailed air-assisted sprayer for bush and tree crops, using the ISO 22866:2005 methodology. The results showed that the limits set are consistent with the values of the spray drift measured and follows the tool’s estimates of low, medium, and high risk of spray drift.

Trajectory deviation of target jet of air-assisted spray under different conditions

Spray characteristics of an air-assisted Direct Injection (DI) injector were studied experimentally by employing high-speed imaging techniques and Phase Doppler Particle Analyzer (PDPA), with particularly interest in the trajectory deviation of target jet. Radial expansion in the near field was observed near the nozzle exit under flash boiling conditions, which can be achieved by decreasing the ambient pressure. The radial expansion in the far field results from the sudden depressurization induce the drastic bubble blast, which improves spray spread and enhances droplet breakup hence influences droplet velocity and size. The radial expansion in the far field, which can be observed in either elevated ambient pressures or low injection pressure conditions, occurs in the far field and results from the interaction of downward and upward gas flow therefore forced the spray plumes outwards. Increasing of the ambient temperature decreases liquid viscosity, leading to the deviation in jet trajectory occurs at the margin of the jet due to the increased vaporization of liquid fuel droplets.

Simulation and Validation of the Air Flow generated by a Multi-Channel Air-Assisted Sprayer

The multi-channel air-assisted spraying can distribute air flow according to the crown diameter and be helpful to improve spray deposition and in the reduction of environmental pollution. However, the factors of air flow distribution are not clear. Computational fluid dynamics (CFD) simulation was used in this paper to investigate the influence of the fan speed (600-1800 rpm) and the distance from the air outlet (0-6.0 m) on the airflow field distribution. The measurements and the simulation results were consistent within the boundary of the test range. The results indicated that the airflow field in the central plane was basically axis-symmetric. The airflow field diffused in the central plane at a certain angle of diffusion. The air velocity first increased and then gradually decreased along the central line, and it displayed an exponential function. Within the range of 1.0 m from the air outlet, there was an obvious section of static air between the adjacent air outlets. Beyond this range, the airflow was well-distributed, and the air velocity was normally distributed at the height y. The airfield generated by the multi-channel sprayer was elliptical in its cross-section from the outlet (for x > 1.0m). The distance of the air supply significantly influenced the fluctuation of the velocity of the airflow, while the speed of the fan had no significant influence on the position of the confluence point of the airflow and the fluctuation of the velocity of each test section.

Design and performance evaluation of a variable-rate orchard sprayer based on a laser-scanning sensor

To improve the precision spraying strategy and reduce excessive pesticide application in orchards, an air-assisted sprayer integrated with a laser-scanning system was developed to realize the toward-target variable-rate spraying. In the spray control system, a method of calculating canopy gridding volumes was designed to ensure the canopy was divided into a uniform grid size, a variable-rate spray model was used in the flow rate decision software to control the spray output according to the canopy gridding volumes and travel speed, and a method of saving and accessing spray data was used to control the spray delay. The effects of different grid sizes and travel speeds on the spray performance were evaluated by quantifying spray coverage uniformity inside tree canopies. The results showed that spray coverage uniformity declined with increasing grid width from 0.14 to 0.28 m although the mean spray coverage on each target location showed no significant differences. Additionally, there were no significant variations in mean spray coverage at speeds of 1.0, 1.2 and 1.4 m/s for a tested tree of 1.6 m width and at any experimental speeds for a tested tree of 1.3 m width, which indicated that the variable-rate sprayer could provide good spray coverage uniformity under various travel speeds with a canopy size limitation. Compared with the same sprayer without the variable-rate spray function, the intelligent sprayer prototype realized effective toward-target spraying and avoided overspraying while providing sufficient spray coverage. Keywords: laser-scanning sensor, variable-rate spray, orchard, precision sprayer, pesticide application efficiency DOI: 10.25165/j.ijabe.20191206.4174 Citation: Cai J C, Wang X, Gao Y Y, Yang S, Zhao C J. Design and performance evaluation of a variable-rate orchard sprayer based on a laser-scanning sensor. Int J Agric & Biol Eng, 2019; 12(6): 51–57.

Spraying strategy optimization with genetic algorithm for autonomous air-assisted sprayer in Chinese heliogreenhouses

Subject to narrow space and large planting density, many advanced crop protection machines are not suitable for Chinese heliogreenhouses. Under these conditions, a novel autonomous air-assisted sprayer is designed to realize automatic spraying and to improve droplet deposition uniformity. With this sprayer, this paper focuses on precise air-assisted spraying control, and a spraying optimization strategy is researched to obtain uniform deposition of droplets on crops. Firstly, the autonomous sprayer and its spraying sub-system are introduced, and the simplified airflow model is constructed and validated via spraying experiments. Furthermore, based on this model, the relationship between droplets deposition area and spraying mechanism posture is deduced, and an offline optimal spraying strategy based on Genetic Algorithm (GA) is proposed. The algorithm encodes 4 key parameters to control the spraying mechanism’s behavior, and the Coefficient of Variation (CV) of droplets deposition on various parts of crops is computed as the fitness value in algorithm iterations. Illustrative optimization processes are simulated, which show the characteristics of uniform spraying solution. With these optimized parameters pre-set in the autonomous sprayer, real spraying tests are carried out in a heliogreenhouse. The results show that the deposition volumes are all in the range of 1.2 ∼ 1.4 μL/cm2. The final CV values of three sets of data are 9.9%, 10.4% and 11.2%, which are small enough for spraying operation. Simulation results and real tests data validated the effectiveness and convenience of the proposed optimal spraying strategy. Finally, some conclusions and future work are discussed. With this spraying strategy optimization, optimized spraying behavior can be planed for different crops with different planting patterns in Chinese heliogreenhouses.

SAAS, a computer program for estimating pesticide spray efficiency and drift of air-assisted pesticide applications

The challenges of ground pesticide applications arise from the increased concerns on potential risks of spray drift to the environment. This paper presents the development of a software application for estimation of spray efficiency and drift from pesticide applications using orchard air-assisted sprayers. The computational fluid dynamics (CFD) simulations provide solutions to the fate and transport of pesticide spray droplets according to crop conditions, spray operating conditions, and weather conditions. The software tool provides the interpolated results based on a drift database generated by CFD simulations, data analysis programs, and condition inputs through graphic interfaces for users. The software enables the users to estimate the spray mass balances, spray drift through airborne and ground deposition by distance, and pesticide drift setback distances to prevent potential risks of spray drift. It is expected to help farmers in making tactical decisions for pesticide applications to enhance the spray efficiency and reduce the risk of spray drift.

Applicability of a 3D Laser Scanner for Characterizing the Spray Distribution Pattern of an Air-Assisted Sprayer

Three-dimensional (3D) laser technology has been tested for assessing the performance of air-assisted spraying. A static test using an air-assisted sprayer equipped with two axial fans (front and back) with opposing directions of rotation was developed. The sprayer was adjusted to spread water in a static mode, at a pressure of 10 bars, with four air volumetric flow rates. Measurements were performed using a Leica HDS6000 3D laser scanner. In addition, the flow and velocity of air generated by the air-assisted sprayer were measured using a hot-wire anemometer and a 3D sonic anemometer with the objective of estimating the influence of air flow on the spatial distribution of spray droplets. To carry out the analysis, all of the droplets detected by the laser were considered to be of the same size. The distribution of products was asymmetric when the machine only worked with the back fan, with 41% of the product distributed on the left side versus 59% on the right side, as referenced to the direction of the machine’s advance. This asymmetry was corrected when the machine functioned with the two fans activated. These spray data were concordant with the measured air flow generated by the machine in the different working conditions. For the different regulation settings of the machine, taking the vertical of the machine as 0°, the angular region comprised between 40° and 60° was the one that received the highest quantity of product. The increase of the air flow produced a greater distance of the product. For the highest air flow configuration, 99% of the product detected by the laser was detected within a distance of 16 m from the axis of the machine.

The influence of guide vane on the performance of an axial fan for air-assisted sprayer

For the axial fan used in air-assisted sprayer, it always requires a good outlet flow field. In addition to ensuring that the outlet flow field has sufficient dynamic pressure, it is also necessary to ensure that the outlet flow direction is close to the axial direction. In this paper, the influence of the profile load distribution and the solidity of the outlet guide vane on outlet flow field was studied with numerical simulation. The results indicates that increasing the solidity or using the fore-load distribution profile can effectively reduce the outlet flow angle, and result in increasing the spraying distance of the water droplet. This result can provide reference for the design of the guide vane for axial fan used in air-assisted sprayer.

A comparative study of three drying methods on drying time and physicochemical properties of chicken powder

ABSTRACTChicken powder produced by hot air drying (HAD), hot air-assisted radio frequency drying (HA-RFD) and spray drying (SD) was obtained. Drying time along with flavor, taste, free amino acid (FAA) content and physico-chemical properties of products were compared. It was resulted that HA-RFD was the fastest means (90 min) with HAD was the slowest (240 min) to achieve target moisture content (under 5%). Concerning product quality, HA-RFD chicken powder exhibited the lowest hygroscopicity (1.80%), best rehydration (137.72%), and better flavor and taste as well as color, and HAD powder exerted best color, solubleness (45.68%) and better rehydration (130.27%). While for chicken powder produced by SD showed the most undesirable color and flavor and highest degree of hygroscopicity (8.40%). Besides, the total FAA content of HA-RFD was the most abundant (3.615 g/100 g), followed by HAD (3.551 g/100 g) and the SD powder had minimum content of total FAA (1.175 g/100 g), which suggested that HA-RFD can reduce thermal quality degradation and improve nutritional value with the lowest damage. Besides, HA-RFD chicken powder had the largest total content of Asp and Glu (3.615 g/100 g), which were the primary contributor to umami. Based on the results, it was concluded that HAD or HA-RFD appeared to be a promising way to prepare for chicken powder.

Influence of canopy development in the vineyard on spray deposition from a tunnel sprayer

Spray deposition from a tunnel, air-assisted sprayer was analysed during the whole season, following canopy development in a vertical-shoot-positioned vineyard. Four field tests were performed using hollow-cone, turbulence nozzles between the BBCH 15 (5 leaves unfolded) and BBCH 77 (berries beginning to touch) growth stages, plus an additional test with flat-fan, air-injection nozzles at BBCH 77. The main canopy parameters were assessed, including the canopy height range (0.6 m to 1.4 m), the leaf area index (LAI; 0.15 to 1.60) and the leaf layer index (LLI; 0.69 to 2.74). Total deposition on target (leaves and bunches) increased from 14.8% to 53.9% of volume applied, and was significantly related to the LLI (R² = 0.943); the relevance of such relationship in connection with the leaf wall area model for volume rate adjustment is discussed in the paper. Losses to the ground (1.9% to 8.1% of volume applied), spray recovery rate (31.0% to 67.2%) and losses owing to evaporation of the recycled liquid (0.1% to 3.5%) were also analysed. At BBCH 77, air-injection nozzles did not improve overall deposition in comparison to hollow-cone nozzles, but increased spray recovery (from 31.0% to 36.1%) and reduced (to 0.1%) evaporation of the recycled liquid, so that they may represent an option to avoid an excessive concentration in the tank towards the end of application.

In-situ open path FTIR measurements of the vertical profile of spray drift from air-assisted sprayers

Estimating pesticide spray drift, which is a part of total drift loss, is complex as airborne pesticide concentrations are low and depend on multiple factors. The aim was to measure and compare vertical profiles of spray drift generated by different sprayers using Open Path Fourier-Transform-Infra-Red (OP-FTIR) spectrometer. Field tests included three types of commercial agricultural sprayers. The OP-FTIR was placed at the edge of an apple orchard with the line of sight parallel to tree rows. The OP-FTIR and its reflector were mounted on platform lifts to allow measurements at 4 heights: 3 (canopy height), 4, 5, and 6 m above ground. The sprayers sprayed water within the three tree rows closest to the OP-FTIR as well as outside each tree row in order to estimate the spray drift as function of distance with and without tree interference. The results of the experiments showed that, under the meteorological conditions prevailing, there were substantial differences between the sprayers in terms of spray drift of droplets with diameter > 5 μm. Additionally, the results showed that spray drift can be reduced substantially (by up to 50%) by using a tree-line barrier or a buffer zone.

Spray Outputs from a Variable-Rate Sprayer Manipulated with PWM Solenoid Valves

Abstract. Pressure fluctuations from air-assisted orchard sprayers can cause nozzles to discharge inaccurate flow rates during variable-rate spray applications. Variations in total flow rate discharged from 40 nozzles, each coupled with a pulse-width-modulated (PWM) solenoid valve, were determined for a variable-rate air-assisted sprayer. Variables for the total flow rate measurements were number of active nozzles ranging from 1 to 40 and PWM duty cycle ranging from 10% to 100%. Experiments were conducted under conditions with and without operating pressure adjustments. Under the no-pressure-adjustment condition, the operating pressure in the spray line was not adjusted for compensation when either the number of active nozzles or PWM duty cycle was changed. Under the pressure-adjustment condition, the operating pressure was adjusted to retain at 242 kPa. The total flow rate increased as duty cycle and/or number of active nozzles increased under both pressure conditions. However, the operating pressure in the spray line dropped considerably as either the number of active nozzles or duty cycle increased under the no-pressure-adjustment condition, resulting in significant lower total flow rates compared to the pressure-adjustment condition. The differences in total flow rates between the two pressure conditions increased as duty cycle and number of active nozzles increased. To improve future intelligent sprayer accuracy, two-variable regression equations were established to predict and control total flow rates with different duty cycles and numbers of active nozzles operated simultaneously. Keywords: Flow control, Flow rate, Hydraulic nozzle, Pesticide, Precision sprayer.

CFD simulation of pesticide spray from air-assisted sprayers in an apple orchard: Tree deposition and off-target losses

The ultimate goal of a pesticide spraying system is to provide adequate coverage on intended canopies with a minimum amount of spray materials and off-target waste. Better spray coverage requires an understanding of the fate and transport of spray droplets carried by turbulent airflows in orchards. In this study, an integrated computational fluid dynamics (CFD) model was developed to predict displacement of pesticide spray droplets discharged from an air-assisted sprayer, depositions onto tree canopies, and off-target deposition and airborne drift in an apple orchard. Pesticide droplets discharged from a moving sprayer were tracked using the Lagrangian particle transport model, and the deposition model was applied to droplets entering porous canopy zones. Measurements of the droplet deposition and drift in the same orchard were used to validate the model simulations. Good agreement was found between the measured and simulated spray concentrations inside tree canopies and off-target losses (ground deposition and airborne drifts) with the overall relative errors of 22.1% and 40.6%, respectively, under three growth stages. The CFD model was able to estimate the mass balance of pesticide droplets in the orchard, which was practically difficult to investigate by measurements in field conditions. As the foliage of trees became denser, spray deposition inside canopies increased from 8.5% to 65.8% and airborne drift and ground deposition decreased from 25.8% to 7.0% and 47.8% to 21.2%, respectively. Higher wind speed also increased the spray airborne drift downwind of the orchard. This study demonstrates that CFD model can be used to evaluate spray application performance and design and operate sprayers with increased spray efficiencies and reduced drift potentials.

Variable air assistance system for orchard sprayers; concept, design and preliminary testing

Conventional air-assisted sprayers with hydraulic nozzles generate large radial spray plumes which produce significant off-target losses and can consume high power (20–30 kW). Also, it is not uncommon to see these machines treating dwarf orchards, where the spray losses at the full leaf stage may be over 80% of applied spray volume. Significant reductions in spray losses can be obtained with targeted and wind-oriented airflow adjustment. The objectives of the presented studies were to develop an energy saving variable air assistance (VAA) system with continuous real-time adjustment of air volume and with spraying systems mounted on both sides of the sprayer. The system is based on a double axial fan system which allows for remote adjustment of air volume. The nominal air output was 20,000 m3 h−1, for use in typical dwarf and semi-dwarf orchards, and this was designed to be obtained with 10 kW power consumption. The system used variable speed impellers with fixed blades which showed greater suitability than a method with adjustable pitch blades working at constant speed because it provided a wider range of air volumes (±35%). The air volumes produced could be continuously adjusted to obtain airflow profiles, on both sides of the sprayer that were almost symmetrical. The results obtained in tests appear to meet the objectives and, therefore, the VAA system can be considered as a suitable prototype platform for variable rate technology and future intelligent orchard sprayers.

Comparative study of CFD models of the air flow produced by an air-assisted sprayer adapted to the crop geometry

A computational fluid dynamics (CFD) model for simulating the air flow produced by an air-assisted sprayer can be developed according to any one of several sets of criteria and for various specific applications. Thus far, most CFD models have focused on the characterization of the air flow generated by the sprayer. However, such models may not be the best when assessing the effectiveness of air-assisted sprayers adapted to crop geometry, such as those used in vineyards. In this study, the air flow produced by an air-assisted sprayer adapted to the geometry of a vineyard was simulated using four CFD models: Model 1 was designed to simulate air velocity measurements at the outlets; Model 2 was designed to simulate air velocity measurements at a certain distance from the outlets; Model 3 was dedicated to the modelling of the internal geometry of the air ducts rather than the characterization of the air flows generated by the sprayer; and Model 4, which was developed as a variant of Model 3, was created to perform the same calculation in several stages. The models were validated with actual measurements of the air velocity near the sprayer outlets. The results showed that although Models 1 and 2 (both of which have been used in most existing studies) simplified the calculation, they are impractical for simulating different air flows. By contrast, Models 3 and 4 provided complex meshes that complicate the convergence of the calculation and require a suitable treatment of both the viscosity and the flow near the walls. Model 3 showed the smallest error (16%) in the air velocity estimated in the treatment plane. Model 4 showed potential for future implementation of the dispersed phase and crop-air interaction because it mitigated the problems arising from the complexity of the meshes. It should also be noted that there are errors inherent to the implementation of the CFD model, errors related to inaccuracies in the geometry of the air ducts, inaccuracies related to the measurement of the air velocities, inaccuracies in the quantification of the air flow, and simplifications linked to the turbulent model.

CFD simulation of airflow inside tree canopies discharged from air-assisted sprayers

Effective pesticide application is not only essential for specialty crop industries but also very important for addressing increasing concerns about environmental contamination caused by pesticide spray drift. Numerical analysis using computational fluid dynamics (CFD) can contribute to better understanding of the transport of spray droplets carried by strong air jets from sprayers. In this research, an integrated CFD model was developed to predict air velocity distributions inside and around tree canopies blown by an air-assisted pesticide sprayer. The sprayer motion was simulated by the sliding mesh technique, and the tree canopies were defined in the computational domain as virtual porous media without their geometric modeling. Validation of the CFD model was accomplished in three steps by comparing the CFD results with previous measurements. Air velocities and airflow pressures downwind from the sprayer agreed well with the measurements when the sprayer was both stationary and in motion. The model was also able to predict accurately the peak air velocity and airflow pressure inside the canopies with average RMS errors of 1.68ms−1 and 0.89kgm−2, and relative errors of 29.2% and 20.2%, respectively. Although discrepancy existed between the field experiment measurement and CFD simulation this study can conclude that the simulation will give a reasonable prediction of air distributions discharged from air-assisted sprayers. The validated CFD model was applied to predict air distribution inside canopies with various canopy dimensions and densities. The complex airflow patterns obtained by the CFD model offered advantages of analyzing effects of various factors on sprayer performance.

Spray pesticide applications in Mediterranean citrus orchards: Canopy deposition and off-target losses

Only a portion of the water volume sprayed is deposited on the target when applying plant protection products with air-assisted axial-fan airblast sprayers in high growing crops. A fraction of the off-target losses deposits on the ground, but droplets also drift away from the site. This work aimed at assessing the spray distribution to different compartments (tree canopy, ground and air) during pesticide applications in a Mediterranean citrus orchard. Standard cone nozzles (Teejet D3 DC35) and venturi drift reducing nozzles (Albuz TVI 80 03) were compared. Applications were performed with a conventional air-assisted sprayer, with a spray volume of around 3000lha−1 in a Navel orange orchard. Brilliant Sulfoflavine (BSF) was used as a tracer. Results showed that only around 46% of the applied spray was deposited on the target trees and around 4% of the spray was deposited on adjacent trees from adjoining rows independently of the nozzle type. Applications with standard nozzles produced more potential airborne spray drift (23%) than those with the drift reducing nozzles (17%) but fewer direct losses to the ground (22% vs. 27%). Indirect losses (sedimenting spray drift) to the ground of adjacent paths were around 7–9% in both cases. The important data set of spray distribution in the different compartments around sprayed orchard (air, ground, vegetation) generated in this work is highly useful as input source of exposure to take into account for the risk assessment in Mediterranean citrus scenario.