H. E. Ozkan

SPRAY CHARACTERISTICS AND DRIFT REDUCTION POTENTIAL WITH AIR INDUCTION AND CONVENTIONAL FLAT-FAN NOZZLES

Spray drift potential, spray coverage, droplet size, and spray pattern width for various sizes of air induction and conventional flat-fan nozzles with equivalent orifice areas were investigated and compared under laboratory conditions. Droplet sizes were measured with a laser imaging system; spray coverage on water-sensitive paper (WSP) was evaluated with a boom sprayer at a constant travel speed in a greenhouse, and ground and airborne spray deposits were determined in a wind tunnel at two wind velocities (2.5 and 5.0 m/s). Tests were also conducted to evaluate the effect of air-intake holes being sealed or open on spray characteristics of air induction nozzles. With the equivalent nominal flow rate, air induction nozzles had approximately 2.1 to 2.75 times larger exit orifice areas than the conventional nozzles. With the equivalent orifice area and equal liquid flow rate, there was no significant difference in droplet size, spray pattern width, spray coverage, ground spray deposit, and airborne deposit among regular air induction nozzles, air induction nozzles with two sealed air-intake holes, and conventional flat-fan nozzles. Spray characteristics of air induction nozzles could be achieved by conventional nozzles with the equivalent orifice size operated at the reduced operating pressure.

Simulation of Drift of Discrete Sizes of Water Droplets from Field Sprayers

The drift distances of water droplets from field sprayers were determined for several variables with a computational fluid dynamics computer program. The simulation variables for drift distances up to 200 m included: droplet size (10 to 2000 mm), wind velocity (0.5 to 10.0 m/s), initial droplet velocity (0 to 50 m/s), discharge height (0.25 to 4.0 m), temperature (10° to 30° C), relative humidity (10 to 100%), and 20% turbulence intensity. Except at low temperature and high relative humidity, all 50-mm-diameter and smaller droplets completely evaporated before depositing 0.5 m below the point of discharge for all simulated conditions. Drift distances increased with increasing wind velocity and discharge height, but decreased with increasing initial downward droplet velocity for 100-mm-diameter and larger water droplets. Changes in ambient temperature and relative humidity had much greater influence on drift distances of water droplets less than 100-mm-diameter than on 200-mm-diameter and larger droplets.

DROPLET SPECTRA AND WIND TUNNEL EVALUATION OF VENTURI AND PRE-ORIFICE NOZZLES

Small- to medium-size droplets are desirable when applying insecticides and fungicides because they provide better penetration into the canopy and better coverage than larger sizes. However, small droplets can drift long distances. Several agricultural nozzle manufacturers have recently introduced so-called “low-drift” nozzles. Although manufacturers of low-drift nozzles claim these nozzles are considerably more effective in reducing spray drift than standard flat-fan nozzles, no independent data are available to support their claim. The objective of this study was to determine the effectiveness of two low-drift nozzles (TurboDrop® and Turbo TeeJet®) in reducing drift. The TurboDrop nozzle design incorporates a venturi air intake port and a pre-orifice chamber while the Turbo TeeJet nozzle design includes only a pre-orifice chamber. Nozzle evaluations were accomplished by measuring droplet sizes with a laser particle sizer and deposition distances of droplets in a wind tunnel (5 m/s). Data from measurements obtained with the low-drift nozzles were compared to data from a standard flat-fan nozzle. The low-drift nozzles produced fewer drift prone droplets and significantly lower downwind airborne deposits than the standard flat-fan nozzle (XR). In general, droplet size measurements taken along the long axis of the spray patterns showed less variation in volume median diameters for the XR and Turbo TeeJet (TT) nozzles than for the TurboDrop (TD) nozzles. The TD nozzles produced lower downwind deposits than TT nozzles operated at similar pressures (276 kPa); however, a larger orifice TT nozzle operated at a lower pressure (176 kPa) produced significantly lower downwind airborne deposits than the TD nozzle operated at 276 kPa. Covering or restricting the venturi air intake port on the TD nozzle increased nozzle output but had little impact on the overall droplet spectrum and downwind drift.

VISUAL AND IMAGE SYSTEM MEASUREMENT OF SPRAY DEPOSITS USING WATER–SENSITIVE PAPER

Water–sensitive papers (WSP) were attached to leaves in nursery trees and sprayed with air–blast sprayers. Deposit patterns on the WSP were rated visually for coverage, from 0 (no spots) to 10 (completely blue). Visual counts of spot density (spots/cm2) were made for cards representing coverage ratings from 1 to 6. WSPs were analyzed with an imaging system; several spot size parameters, number of spots, and area coverage percentage were measured. Visual ratings of 6, 7, and 8 had considerable variability in area coverage percentage. Sample WSPs with visual coverage ratings of 3, 5, 6, and 8 and minimum, median, and maximum coverage percentages are presented. Visually measured spot density was greater than image–system measured spot density for all rating numbers, especially for higher spot densities. Spot density began to decrease at visual rating numbers greater than 7.

Evaporation and Deposition Coverage Area of Droplets Containing Insecticides and Spray Additives on Hydrophilic, Hydrophobic, and Crabapple Leaf Surfaces

The efficiency of foliar spray applications is influenced by the evaporation and residual pattern of pesticide droplets on targets. Evaporation time and maximal coverage area of a single droplet from 246 to 886 m in size at relative humidity (RH) ranging from 30% to 90% were measured with sequential images under controlled conditions. Droplets were placed on targets inside an environmentally controlled chamber under a stereoscope and a high-definition digital camera. The spray mixtures used to form droplets included different combinations of water, a nonionic colloidal polymer drift retardant, an alkyl polyoxyethylene surfactant, and two commercially available insecticides. The droplet evaporation was investigated on crabapple leaf surfaces, and hydrophilic and hydrophobic glass slide surfaces. Adding surfactant into spray mixtures greatly increased droplet coverage area on the surfaces, while droplet evaporation time was greatly reduced. For a 343 m droplet on a crabapple leaf at 60% RH, the evaporation time decreased from 70 to 50 s and the maximal coverage area increased from 0.366 to 0.890 mm 2 after the surfactant was added into the spray mixture containing water and insecticide. Adding the drift retardant into the spray mixture slightly increased the droplet evaporation time and decreased the droplet coverage area. In addition, changing the target surface from the hydrophilic slide to the hydrophobic slide greatly increased the droplet coverage area and reduced the droplet evaporation time. Increasing RH increased the droplet evaporation time greatly but did not change the coverage area. The droplet evaporation time and coverage area increased exponentially as the droplet size increased. Therefore, droplet size, surface characteristics of the target (waxy or non-waxy), RH, and chemical composition of the spray mixture (water alone, pesticide, additives) should be included as important factors that can affect the efficacy and efficiency of pesticide applications.

DETERMINING THE INFLUENCE OF SPRAY QUALITY, NOZZLE TYPE, SPRAY VOLUME, AND AIR-ASSISTED APPLICATION STRATEGIES ON DEPOSITION OF PESTICIDES IN SOYBEAN CANOPY

Field studies were established in north central Ohio to determine the effect of different application strategies on targeting of foliar pesticides in narrow-row (18 cm) soybeans. Several different application factors were tested, including spray quality, nozzle type, air-assistance, and spray volume. In 2005, the spray mix included a fungicide. In 2006, in addition to the fungicide, an insecticide was included. Plant samples were removed from each test plot, and stems and leaves from the bottom third and middle third of the plant were separated for analysis. Overall, there was significantly less active ingredient found in the lower third of the canopies than the middle third, and significantly less pesticide residue was found on stems than leaves from the same canopy location. Significantly more fungicide residue was found on lower leaves treated by the medium-quality XR8004 flat-fan nozzle in 2005 than the coarse-quality XR8005 flat-fan nozzle. There were no differences in fungicide residue found on middle canopy leaves between the fine, medium, and coarse quality flat-fan nozzles. The twin-fan pattern nozzles (Turbo Duo and TwinJet) produced the lowest amounts of fungicide residue on the lower leaves in 2005. The mechanical canopy opener produced significantly higher fungicide residues on middle canopy leaves than all other treatments. The Jacto air-assist sprayer using JA3 hollow-cone nozzles produced the highest fungicide residues on lower canopy leaves in 2005. There were some statistical differences between the amounts of fungicide and insecticide residue found on plant tissue in 2006 because of the high amount of variability in the sample data. Overall in 2006, the higher volume XR8004 treatment (187 L ha -1 ) and the twin-fan TTJ60-11003 treatment at 145 L ha -1 performed similar to the Jacto sprayer making applications at 145 L ha -1 using either flat-fan or hollow-cone nozzles. In general, higher volume applications produced higher amounts of fungicide and insecticide residue on leaves from the middle of the canopy for conventional flat-fan and air-assist applications. Spray volume had less affect on residues measured on leaves from the lower canopy area. Across two years of different canopies at the same spray volume (145 L ha -1 ), the Jacto sprayer using JA3 hollow-cone nozzles produced more fungicide residue on middle canopy stems and lower canopy leaves than the medium-quality XR8004 flat-fan nozzle.

Fluorescent Intensity of Dye Solutions under Different pH Conditions

Fluorescent tracers are widely used for assessment of spray quantity in the field due to their relatively high sensitivity, low cost and user safety. However, many concerns have been raised over their measurement accuracy due to questions of stability of fluorescence during tests. Stable analysis of fluorescence is essential to ensure accurate evaluation of pesticide spray application efficiency. The objective of this research was to determine the stability of fluorescent intensity of five tracers dissolved in solutions with various pH conditions in an effort to minimize analytical errors in the measurement of spray deposition and drift. The fluorescent intensity of five fluorescent tracers commonly used for the quantitative assessment of spray deposition and off-target loss was investigated with wash solutions over pH conditions from 6.9-10.4. The tracers selected in the tests were Brilliant Sulfaflavine (BSF), Fluorescein, Pyranine, Tinopal, and Eosin. The fluorescence of Pyranine was the most sensitive to the solution pH conditions, followed by Fluorescein and Tinopal, while BSF and Eosin had a nearly constant fluorescent intensity over the pH range from 6.9-10.4. The fluorescence of Fluorescein increased 1.3 times, Tinopal 1.25 times, and Pyranine 3.0 times as the pH value increased from 6.9- 8.4, but it became nearly constant when pH value was greater than 8.4. However, Pyranine, Fluorescein, and Tinopal showed much stronger fluorescence than BSF and Eosin. A solution containing Fluorescein at pH 8.4 and higher demonstrated 83 times greater fluorescent intensity than the solution containing the same amount of BSF. In conclusion, the fluorescence of tracers should be examined under various pH conditions during the selection of tracers for pesticide spray deposition and drift trials.

FOLIAR DEPOSITION AND OFF-TARGET LOSS WITH DIFFERENT SPRAY TECHNIQUES IN NURSERY APPLICATIONS

Information is lacking on spray techniques to improve deposit uniformity within nursery canopies and reduce off-target loss on the ground and via spray drift from the treated area. Spray deposits at various elevations within crabapple trees and on the ground were investigated with an air blast sprayer equipped with conventional hollow-cone nozzles, air-induction nozzles, and conventional hollow-cone nozzles with a drift retardant in a commercial nursery field. Airborne deposits at three elevations on sampling towers and on the ground at several distances from the sprayer were also investigated with the three spray treatments in an open area without trees. To compare field test results, wind tunnel experiments were conducted to assess spray deposits on the floor beyond 0.4 m downwind distance from the nozzles and airborne deposits at 2.1 m downwind from the spray discharge point with the three spray techniques without air assist. Droplet size distributions across spray patterns without air assist were measured with a laser particle/droplet image analysis system. In general, there was no significant difference for deposits within nursery tree canopies and on the ground with three different spray techniques. At the 700 L/ha application rate, which was 360 L/ha lower than the rate typically used in nursery application, the tree canopies received over 4 to 14.5 times as much spray deposit as actually needed from all treatments, and a large portion of spray volume deposited on the ground. Compared with conventional hollow-cone nozzles, drift reduction from air-induction nozzles or the spray mixture with drift retardant treatment was significant in wind tunnel tests but was not significant in field tests.

VIABILITY OF A BIOLOGICAL PEST CONTROL AGENT THROUGH HYDRAULIC NOZZLES

Exposure to hydrodynamic stresses during flow through a hydraulic nozzle can cause permanent damage to biological pesticides during spray application. Aqueous suspensions of a benchmark biological pest control agent, entomopathogenic nematodes (EPNs), were passed through three different hydraulic nozzles (standard flat fan, Spraying Systems XR8001VS; hollow cone, Spraying Systems TXA8001VK; and full cone, Spraying Systems FL5-VS) within an experimental, opposed-pistons flow device. Computational fluid dynamics (CFD) was used to numerically simulate the internal flow within the XR8001VS and TXA8001VK nozzles, and important flow field parameters from the CFD simulations were compared to the observed EPN relative viability after treatment. Overall, greater reductions in EPN relative viability were observed for the flat fan (9.5%) compared to the cone type nozzles (<2.8%). The average energy dissipation rates within the exit orifices were significantly higher for the XR8001VS flat fan compared to the TXA8001VK hollow cone, which was consistent with the greater reductions in EPN relative viability observed for the XR8001VS. These differences in EPN damage were due to the distinct characteristics of each nozzle’s flow field. The reduced flow area of the narrow, elliptical exit orifice of the flat fan generates an extensional flow regime, where it was found that the tensile stresses developed were large enough to cause nematode damage. However, with the cone nozzles, the high rotational flow component did not produce hydrodynamic conditions conducive to causing nematode damage. Overall, common hydraulic nozzles were found to be acceptable for spray application of EPNs following the manufacturer’s recommendations. However, it is recommended that an appropriately sized (i.e., larger than the organism) cone nozzle is more suitable for spray application than a fan nozzle to avoid damage to the biopesticide.

Effect of Orifice Wear on Spray Patterns From Fan Nozzles

The effects of nozzle wear on the spray patterns of fan nozzles made with different materials and capacities were investigated. An automated computerized weighing system was developed to rapidly evaluate the spray deposit distribution from the nozzles. Results indicate there was some difference between spray deposit distributions of new and worn fan nozzles. The width of the spray pattern remained nearly constant but worn nozzles delivered greater volumes of liquid in the centers of the spray patterns.