R. D. Fox

Coverage and Drift Produced by Air Induction and Conventional Hydraulic Nozzles Used for Orchard Applications

A conventional, axial-flow, air-blast orchard sprayer was used to make applications to the outside row of a semi-dwarf apple block. Fluorescent tracer was applied at the same rate using either disc-core nozzle sets or air-induction nozzles fitted with flat-fan tips. The experiment included measuring the percent area of spray coverage on leaves after three variations in spray application method. Each of the variations used a different type of nozzle on the same conventional, axial-fan orchard sprayer. The three nozzle variations were a Spraying Systems D3-25 nozzle set, a Spraying Systems D4-25 nozzle set, and a TurboDrop 02 (TD02) air-induction nozzle set. Canopy spray deposits, downwind sedimentation, and airborne spray losses were also measured following treatment on the inside half of the outside row using D4-25 nozzles or TD02 nozzles. The small droplet spectrum D3-25 nozzle set produced the highest leaf surface coverage on both upperside and underside surfaces at 2.0 and 3.0 m heights in the canopy. The upperside leaf surface coverage produced by the D3-25 nozzle was only somewhat greater than the TD02 nozzle. It was, however, significantly higher than the D4-25 nozzle set at the 3.0 m height. Conversely, the underside leaf surface coverage produced by the D3-25 was significantly greater than the TD02 nozzle set at both 2.0 and 3.0 m heights and not statistically different from the D4-25 nozzle set at the lower sampling height. There were relatively few differences in canopy spray deposits between the D4-25 and TD02 nozzle sets. The TD02 treatment produced the lowest downwind sedimentation deposits on targets 8 to 32 m from the edge of the orchard. The D4-25 produced approximately three times higher deposits up to 9 m above the ground than the TD02 treatment on passive nylon screens located 8 m downwind from the edge of the orchard. The D4-25 treatment produced significantly higher airborne deposits on elevated, high-volume, air sampler filters out to 64 m. At 128 m, sedimentation and airborne deposits were similar for the D4-25 and TD02 treatments.

Computer Simulation of Variables that Influence Spray Drift

A computer program was used to determine the effects of several variables on drift distances of spray droplets. Variables were initial droplet size, velocity and height of discharge, wind velocity, turbulence intensity and relative humidity, and volatility of the liquid. For relative humidity and wind velocity ranges of 20-80% and 0.5-4.0 m/s, all water droplets 50 µm diameter and smaller that were directed downward with initial velocity of 20 m/s either completely evaporated or drifted farther than 6 m before depositing 0.5 m below point of discharge. With 20 m/s initial droplet velocity, 2.0 m/s wind velocity (20% turbulence intensity) and 60% relative humidity, 100 and 200 µm diameter droplets deposited at mean distances from point of discharge of 2.6 and 0.13 m respectively. Drift distances of water droplets as large as 200 µm diameter were influenced by initial droplet velocity and height of discharge. Experimental data verified the accuracy of the computer program in predicting drift distances of water droplets.

A History of Air-Blast Sprayer Development and Future Prospects

The design and operating procedures of air-blast sprayers have been greatly improved over the past 50 years. Early tree and vine spray application equipment used hand-guns that required a large amount of water. Later, sprayers with efficient fans, producing large volumes of air at high velocities, were developed for large fruit and nut trees. Recently, apple growers have planted many dwarf and semi-dwarf trees. In general, it is easier to produce more uniform coverage with less drift when spraying small trees than when spraying large trees. Modern designs such as tower, directed jet, and tunnel sprayers should reduce airborne spray drift and produce more uniform coverage. For optimum effectiveness, sprayer air-jet velocity, volume, and droplet spectra should be matched to the tree size, shape, and density. Besides optimizing delivery parameters, future sprayers will likely be required to handle biological materials with a greater variety of physical properties than the standard chemical materials used now. In addition, these materials will require spray systems that protect the live spray products from damage from heat, mechanical stress, and other factors that may kill the beneficial organism being applied.

Using a videographic system to assess spray droplet impaction and reflection from leaf and artificial surfaces

A video motion analysis system was used with two different monodisperse droplet generators to quantify droplet impaction and any consequent reflection. By using different magnification/droplet generator combinations, droplet impaction was detailed at various stages. Low (7×) magnification, together with a generator that produced a spray cloud, allowed determination of the height and numbers of droplets reflected from plant surfaces. Higher (15×) magnification and a single-drop generator enabled the trajectory, and changes in velocity, of a rebounding droplet to be followed. By using high (90×) magnification and the single-drop generator, detailed measurements of a droplet deforming on impact could be made. Examples of how these techniques could be used are given.

Wind Tunnel Evaluation of a Computer Program to Model Spray Drift

A computer program (Fluent“) was evaluated for use in modeling the drift of spray droplets delivered by atomizers. A uniform-size droplet generator and wind tunnel were also used to determine drift distances for various droplet sizes, wind velocities and other operating conditions. Drift distances determined experimentally for droplet sizes ranging from 148 to 424 mm diameter and wind velocities ranging from 0.5 to 6.2 m/s agreed well with distances predicted by the computer program.

Downwind Residues from Spraying a Semi-dwarf Apple Orchard

Airborne spray and ground deposits were measured downwind from a row of semi-dwarf apple trees sprayed with an orchard air sprayer. Airborne spray collectors used were: string, plastic tape, bottles, and high-volume air-sampler filters; collector locations were at 7.5 to 240 m from the tree row, 0.5- to 10-m elevation. Ground deposits were collected on lines perpendicular to the tree row and at distances from 3 to 240 m downwind from the tree row. A mixture of water and a fluorescent tracer was sprayed on the trees at 468 L/ha during a total of 16 passes on four days and climatological data were recorded.

Downwind residue from air spraying of a dwarf apple orchard.

ABSTRACT The edge row of dwarf apple trees was sprayed with an air sprayer; fluorescent dye was used to trace spray drift deposits. Tracer deposited on the ground was measured with plastic collectors and airborne spray was captured and measured with string, bottle, and high-volume, air-sampling filter collectors. Microclimatic variables including vertical heat flux were measured. Ground deposit decreased greatly beyond 120 m; about 0.03% of total material sprayed was deposited between 122 and 152 m downwind. Airborne spray between the ground and a 20 m level at 122 m downwind was estimated to be about 3.5%. Ground collectors and an unobstructed array of string collectors located 5.0 m from the sprayer captured about 75% of the total material sprayed.

A System to Evaluate Shear Effects on Spray Drift Retardant Performance

A laboratory system was developed to simulate shear on mixtures of water and drift retardants due to their recirculation in sprayer tanks. Three significantly different drift retardants (AgRHO DR-2000, Nalco-Trol and Nalco-Trol II) were evaluated in both a Myers A36 orchard airblast sprayer and the laboratory system. Droplet size distributions of sprayed samples from the sprayer and the laboratory system were measured with an Aerometric Phase/Doppler Particle Analyzer. Droplet size distributions of sprayed samples with drift retardants sheared with the laboratory system had similar trends to those of samples sheared with the airblast sprayer as the number of recirculations increased. When the number of recirculations through the system increased from 0 to 11.4, DV0.5 of sprayed samples of the 0.1% DR-2000 mixture did not change significantly from the initial value of 587 mm, but DV0.5 of sprayed samples with 0.0547% Nalco-Trol and the 0.0547% Nalco-Trol II mixtures decreased from 592 to 422 mm and from 505 to 366 mm, respectively. Also, the percent spray volume < 200 mm for mixtures with DR-2000 and Nalco-Trol taken after 11.4 recirculations was 72.8 and 34.1% less than that of a water spray. A possible test system for an ASAE standard is presented.

Surfactant Diffusion and Dynamic Surface Tension in Spray Solutions

In spray application, reflection (rebound) and wetting difficulty can hinder droplet retention by plant surfaces. Surfactants are usually added to formulations to help overcome these problems, but are sometimes ineffective. Some workers have found dynamic surface tension (DST) to be more reliable than equilibrium surface tension (EST) as a measure of surfactant effectiveness. Diffusion-controlled surfactant adsorption generally produces the quickest surface tension reductions as newly generated interfaces age. A diffusion model was developed for DST of three surfactants representing those commonly used in agrochemical formulations: Tween 20, Triton X-100, and Triton X-405. A bulk-solution diffusion model was developed which, together with the DST model indicated apparent diffusive surface-layer thicknesses of a few micrometers. Apparent diffusion coefficients were determined from DST data obtained by oscillating-jet and maximum bubble pressure methods for aqueous solutions. Good agreement of the models with DST data indicated that adsorption processes for the surfactants were diffusion-controlled. Surface ages required to achieve EST for the surfactants were greater than time intervals observed for droplet deformation and recovery in impaction.

Performance Evaluation of a Newly Developed Variable-Rate Sprayer for Nursery Liner Applications

An experimental variable-rate sprayer designed for liner applications was tested by comparing its spray deposit, coverage, and droplet density inside canopies of six nursery liner varieties with constant-rate applications. Spray samplers, including water-sensitive papers (WSP) and nylon screens, were mounted inside tree canopies to collect spray deposit and coverage from variable-rate and constant-rate (555 and 1,110 L ha-1) applications. Models for estimating spray volume savings of the variable-rate sprayer compared to constant-rate and tree-row-volume (TRV) rate applications were developed for various liner canopy sizes and tree spacings. The accuracy of the model was validated with the field test data. For the liner trees tested, the variable-rate sprayer delivered 151 to 359 L ha-1 application rates, while the conventional constant-rate application required 1,110 L ha-1. Due to substantially lower spray output, the variable-rate application had lower (but sufficient) spray deposit, coverage, and droplet density than the constant-rate applications. The variable-rate application also had significantly less variations in spray deposit within canopies of different-size trees. Test results showed that the variable-rate sprayer reduced spray volume by up to 86.4% and 70.8% compared to the 1,110 L ha-1 and TRV-based rate applications, respectively, while the model-estimated savings were up to 94.6% for the 1,110 L ha-1 application and 57.7% for the TRV-based rate applications. Therefore, the newly developed variable-rate sprayer would bring great reductions in pesticide use and safeguard the environment for nursery liner production.