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.     

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.     

Herbicide coverage in narrow row soybean as influenced by spray nozzle design and carrier volume

The use of reduced drift nozzles that produce larger droplet sizes that are less prone to drift will likely be required for use of future postemergence herbicide applications in soybean in the USA. Experiments to evaluate the effect of reduced drift spray nozzles on spray solution coverage were conducted in the field in Indiana. Air induction extended range (AIXR) and turbo TeeJet air induction (TTI) nozzles that produce extremely coarse to ultra coarse droplets were compared to extended range (XR) and Turbo TeeJet (TT) nozzle that produced fine to coarse droplets. Each nozzle was evaluated for spray coverage at 94 and 140 l ha⁻¹ spray volumes using water sensitive cards. Precipitation varied between site years and resulted in differences in soybean canopy development and spray solution coverage. Coverage was greater at the top of the canopy than at the bottom of the soybean canopy as expected. An interaction occurred at the top and middle of the canopy in which the AIXR and TTI nozzles had similar coverage between the two spray volumes, whereas the XR and TT nozzles had greater coverage at 140 l ha⁻¹ carrier volume than 94 l ha⁻¹ carrier spray volume. Spray solution coverage at the bottom of the canopy, where target weeds would be, was similar between all nozzle types. Coverage was greater at the bottom of the canopy at 140 l ha⁻¹ spray volume than with the 94 l ha⁻¹ carrier volume. Spray volume has a greater influence on coverage than spray nozzle type and AIXR and TTI nozzles are less prone to coverage differences due to spray volume than the XR and TT nozzles.     

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.     

Deposition characteristics and biological effectiveness of fungicides applied to winter wheat and the hazards of drift when using different types of hydraulic nozzles

Hydraulic-fan cone, low-pressure fan and two-chamber cone nozzles were used at 1.5, 3.0 and 6.0 bar (150, 300 and 600 kPa) to deliver 140, 200 and 3001 ha⁻¹ respectively of a fungicide spray to control mildew and yellow rust in winter wheat. No significant differences in biological effect were obtained although fan nozzles deposited significantly more on the upper parts of the stems, and two-chamber cone nozzles deposited less on the flag leaf and on the upper part of the stems. Because of their higher deposit and more even distribution, fan nozzles should be preferred, operated at a pressure of 1.5–3 bar to deliver a spray volume of 140–190 lha⁻¹ at 7 km h⁻¹ and to obtain an acceptable biological effect. Higher pressure (6 bar) and volume rates gave no improvement in fungicide performance. Adding a surfactant or penetration oil did not change the volume median diameter or proportion of spray liquid in droplets < 150 μm. Less drift was found when using two-chamber cone nozzles at 3 bar than with flat-fan spray nozzles at 1.5 bar. It is concluded that the two-chamber cone nozzle is useful for fungicide application when drift must be avoided.     

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.     

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.     

Effects of sprayers and nozzles on spray drift and terminal residues of imidacloprid on wheat

In pesticide application, it can be obtained by using appropriate nozzles and sprayers to reduce spray drift and pesticide residues. In this study, a field trail was conducted to determine the spray drift and pesticide residue of imidacloprid on wheat, using three types of flat fan nozzles from the LECHLER Company (LU120-02, AD120-02, IDK120-02) and two types of sprayers (guided-baffle shield sprayer (GBSS) and conventional sprayer (CS)). The spray drift (measured with both airborne and sediment samplers) and terminal residues on wheat were analyzed by liquid chromatography triple-quadrupole mass spectrometry. The results show that both the sediment drift and airborne spray profile were greatest for the LU120-02 nozzle, intermediate for the IDK120-02 nozzle, and lowest for the AD120-02 nozzle. The shielded sprayer gave one third of the drift recorded by airborne samplers and one half of the drift recorded by sediment samplers, compared with results from the CS. Airborne spray drift decreased with increasing height. The imidacloprid residues on wheat grain from different application methods were all below the maximum residue limit (MRL) suggested by EU (0.1 mg/kg) or China (0.05 mg/kg) and no imidacloprid residue was detected on wheat straw. Considering the factors on environment protection, food safety, and biological efficacy, the AD120-02 nozzle and GBSS performed better compared with other nozzles and sprayers. The combination of AD120-02 nozzle with a GBSS is likely to be the optimum application method on wheat.     

Determination of drift potential of different flat fan nozzles on a boom sprayer using a test bench

This study's objective was to evaluate the functionality of an ad hoc test bench for spray drift measurement with boom sprayers, using it for evaluating different nozzles according to drift risk. The repeatability of results was evaluated by conducting similar tests at two different laboratories. Drift potential values (DPV) obtained showed an interesting effect of Venturi flat fan nozzles on drift reduction, in comparison with conventional flat fan nozzles (reference nozzle was XR 11003). Newly designed flat fan nozzles reduced the risk of drift. Reasonably relations between 10th-percentile, D[v,0.1], 50th-percentile or Volume Median Diameter, D[v,0.5], 90th-percentile, D[v,0.9], V₁₀₀ and DPV were observed in all cases, with R² values of 0.58, 0.65, 0.66 and 0.72, respectively. The lowest drift values were achieved with TTI and TD Spray Max nozzles; they were significantly lower than those obtained for IDK and AIXR ones. Results indicated that the drift test bench can be used as an alternative to the official standard procedure for drift measurements on boom sprayers (e.g. ISO 22866), as it is able to discriminate the influence of different boom settings (especially nozzle types) on drift. Further studies could be useful in order to prove that the classification of nozzles according to drift risk obtained using the test bench is comparable to the nozzle classifications obtained applying the ISO 22866 test method.     

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.     

Contribution of spray droplet pinning fragmentation to canopy retention

Drop behaviour during impact affects retention. Increasing adhesion is usually seen as an objective when applying crop protection products, while bouncing and shattering are seen as detrimental to spray retention. However, observation of drop impacts on barley (Hordeum vulgare L.) using high speed shadowgraphy shows that bouncing and fragmentation can occur in Cassie–Baxter as well as in Wenzel wetting regimes. In this last regime, a part of the drop may remain stuck on the surface, contributing to retention. Using simultaneous measurements of drop impacts with high speed imaging and of retention with fluorophotometry for spray mixtures on excised barley leaves using a Teejet 11003 nozzle at 0.2 MPa, it was observed that about 50% of the drops that fragmented in the Wenzel state remain on the horizontal leaf. Depending on the spray mixture, these impact outcomes accounted for 28–46% of retention, the higher contribution being correlated with bigger VMD (Volume Median Diameter). This contribution is not negligible and should be considered when modelling spray retention processes.     

A vertical spray boom application technique for conical bay laurel (Laurus nobilis) plants

Bay laurel, a commercially grown evergreen ornamental plant and economically important for Flanders (Belgium), is very susceptible to pests. Pest management usually consists of spraying pesticides using handheld application techniques which are labour-intensive, involve a high risk for operator exposure, and provide only suboptimal biological control. One alternative, a vertical spray boom, was evaluated in a bay laurel crop pruned into a conical shape. Different spray boom configurations were by attaching water-sensitive papers to a model that emulated the size and shape of the trees. The optimal nozzle type was determined by deposition measurements in an actual laurel crop. Three application rates were tested, 2450, 4900 and 7200 L ha⁻¹ of ground surface. The most efficient spray application technique was found to be an extended range flat fan, an air included flat fan or a hollow cone nozzle, all at 4900 L ha⁻¹ resulting in the highest relative spray deposits and the most uniform spray distribution in the canopy.     

Comparative droplet-size spectra for three different-angled flat fan nozzles

Droplet-size spectra for 110-, 80- and 65-degree flat fan nozzles of equal output were measured at distances 5–45 cm from the nozzle using a laser diffraction system. The volume median diameters (VMDs) decreased between 5 and 20 cm from the nozzle and increased with distance at distances greater than 30 cm. Similarly, the proportion of small droplets in the spray was greatest at about 20 cm with subsequent reduction with distance. The VMDs at each distance decreased with increasing nozzle angle and the corresponding percentage of small droplets increased. Addition of wetting agent had little effect up to 0·01% v/v. Increasing concentrations lowered the VMD and raised the percentage of small droplets.     

Effect of the nozzle adaptor of sprayer calibrator on flow rate measurements

To ensure the proper use of plant protection products, the European Directive 2009/128/CE requires sprayer inspection throughout Europe. The required tests and methods for inspection of agricultural sprayers are outlined in the European Standard EN 13790: 2003 in which nozzle flow rate measurement is one of the main requirements. Currently, most of the sprayer inspection workshops are equipped with a nozzle flow rate measurement device which consists of air-tight nozzle adaptors connected to 2-3 m hoses which discharge to a bank of graduated cylinders. However, these adaptors block the air holes of the air-induction nozzles, disrupt the spray atomization and change nozzle output. The main objective of this study was to investigate the variation of nozzle flow rate due to the use of air-tight adaptors. A series of nozzle flow rate measurements were made using different kinds of nozzle adaptors with various sizes of air induction, extended range and Turbo TeeJet^® nozzles.The use of air-tight nozzle adaptors increased the flow rates of air induction and extended range nozzles. Plugging the air holes of air-induction nozzles increased the flow rate. The increase in flow rate decreased with nozzle pressure. Overall, the magnitude of the flow rate increase depended on the nozzle type but remained constant for all of the same type. These differences should be accounted for in sprayer calibration.     

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.     

Effects of Fusarium culmorum and water stress on durum wheat in Tunisia

The effects of water stress on Fusarium foot and root rot in durum wheat were investigated in growth chamber, greenhouse and field tests in Tunisia. In the seedling stage, emergence of six durum wheat cultivars in the growth chamber was significantly reduced by inoculation with Fusarium culmorum and water stress (P<0.0001), with more disease under drier conditions. Additionally, the tiller number per mature plant, the 1000 grain weight and disease severity in mature stage were reduced by inoculation in greenhouse studies. In a field test, inoculation with F. culmorum significantly reduced the yield (P<0.001), by more than 17% for Om Rabiaa and 38% for Karim, the two cultivars tested. Yield was also significantly affected by precipitation and irrigation levels. The severity of the disease, estimated by the percentage of white heads, was separately affected by the cultivar (P<0.001) and inoculation (P = 0.0004). Percentage of white heads was 1.5 and 2 × higher in inoculated plants than non-inoculated for Om Rabiaa and Karim cultivars, respectively. Disease severity was highest in treatments with the greatest water stress. This is the first detailed study of water stress and F. culmorum on durum wheat in Tunisia, and indicates that cultivar resistance and irrigation management may be important in the management of Fusarium foot rot.     

Spray interactions with a windbreak netting used in orchard applications

An extruded plastic windbreak netting, with an optical porosity of 64%, was used to evaluate its potential in reducing sprayer air velocity and intercepting spray droplets in simulated orchard applications. The air velocity reduction was assessed in laboratory tests carried out under static and dynamic conditions. In field tests, the netting was directly sprayed with two orchard airblast sprayers, equipped with different nozzle types.Air velocity reduction was higher in the dynamic setting but decreased at lower air velocities. It also decreased when the netting distance from the air outlet increased. In field tests, the analysis of spray fallout depositions in open area conditions revealed lower recovery rate for conventional than air induction hollow cone nozzles. Comparing the fallout collected on sampling lines (perpendicular to the sprayer travel path) behind the netting and in the open area showed an average spray retention of 30.5% for the netting. The netting affected the fallout pattern along the sampling line, showing a droplet trajectory deflection associated with the momentum and kinetic energy losses. An increase of ground deposition was noticed just behind the netting (up to 2 m). At farther distances ground deposits decreased considerably. The results showed the potential for using a windbreak netting to simulate the droplet retention characteristics of a hypothetical tree foliage, in order to reduce the effect of canopy variability in certain orchard applications studies.     

The effect of combined application of the entomopathogenic fungus Metarhizium anisopliae and the release of predatory mite Phytoseiulus longipes for the control of the spider mite Tetranychus evansi on tomato

The entomopathogenic fungus Metarhizium anisopliae (Ma) and the predatory mite Phytoseiulus longipes (Pl) are both potential biocontrol agents of the tomato spider mite Tetranychus evansi. The combination of the two agents may enhance biological control of T. evansi if there is no antagonistic effect. Here, we evaluated the effect of combining the application of Ma and Pl in the control of T. evansi under screenhouse and field conditions on tomato crops. The acaricide abamectin was included as a control. Spray applications of Ma and abamectin, and release of Pl in the screenhouse significantly reduced mite population density among motile (P < 0.0001) and egg stages (P < 0.0001) of T. evansi as compared to the control. There was also significant reduction in mite population density in the field but only with spray applications of Ma and abamectin, and Ma + Pl treatments among motile (P < 0.0001) and egg stages (P < 0.0001). In the screenhouse experiment, leaf damage was significantly lower in all the treatments than in the control. In the field, leaf damage was significantly higher in the control and Pl alone treatments than in the other treatments. The combination of both Ma and Pl resulted in a reduction of T. evansi numbers in the screenhouse and field, but did not consistently differ significantly from Ma alone. Based on these results, we conclude that there is no benefit of combining M. anisopliae and P. longipes for the control of T. evansi in tomato crops.     

Sprayer type and water volume influence pesticide deposition and control of insect pests and diseases in juice grapes

In a mature Vitis labrusca L. “Niagara” vineyard, we compared an airblast sprayer and an air-assisted rotary atomizer (AARA) low-volume sprayer for coverage of grape clusters and control of grape berry moth, Paralobesia viteana. In addition, the effect of spray volume on control of fungal diseases was evaluated using the fungicides ziram and azoxystrobin applied with an airblast sprayer. For evaluation of coverage, sprayers applied kaolin clay at 28 kg/ha to grapevines while operating at low, medium and high water volumes. Kaolin residues on grape clusters were analyzed to compare the total amount of spray material deposited, percent of fruit surface covered, number of deposits, size of deposits and distance between deposits. There were no significant differences between sprayers or water volumes in the total amount of kaolin deposited on clusters, but the percent surface coverage was much greater on outside-facing berry surfaces (facing the sprayer) than inside-facing surfaces (facing the rachis). On the outside-facing berry surfaces, the airblast sprayer at 468 L/ha of water (medium volume) provided the highest percent coverage, the greatest density of deposits, the largest deposit diameter, and the smallest distance between deposits. On the inside-facing berry surfaces, the same sprayer–volume combination provided the highest percent coverage and greatest deposit diameter, but deposits from the airblast sprayer operating at 935 L/ha (high volume) had the smallest distance between deposits. No significant differences between sprayers or among water volumes were detected in the deposit density on the inside-facing berry surfaces. Bioassays of grape clusters sprayed with fenpropathrin or methoxyfenozide using the airblast or AARA sprayers at two water volumes revealed the greatest fruit protection from P. viteana at the higher volume for the airblast sprayer, but at the lower volume for the AARA sprayer. Spray volume of the airblast sprayer also affected disease control by the protectant fungicide ziram more than by the systemic fungicide azoxystrobin, with 468 L/ha providing better control than 187 L/ha. However, for most diseases, fungicide type was more influential than spray volume in determining the disease control outcome. The results of this study emphasize the need for appropriate water volumes relative to the sprayer and pesticide being used to optimize pest and disease control in juice grape vineyards.