J. B. Ross

DISPERSION OF FINE SPRAY FROM AERIAL APPLICATIONS IN STABLE ATMOSPHERIC CONDITIONS

A field study of aerial spray movement and dispersion was conducted at the New Mexico State University spray study site on the USDA Jornada Desert research ranch in April 2005. The purpose of the study was to measure the plume movement and in-plume spray concentrations of very fine droplets applied during calm, stable atmospheric conditions. Spray plume movement and dispersion were measured and recorded with a portable elastic-backscatter lidar. Supporting meteorology and air turbulence measurements were made simultaneously with 3-D sonic anemometers. A Cessna T188C equipped with Micronair AU5000 rotary atomizers produced small droplets (volume mean diameter of 37.3 µm). The amount of spray material remaining in the air decreased rapidly for 1 to 2 min, and thereafter remained nearly constant and drifted as a definable plume with the slight air currents.

ATMOSPHERIC STABILITY EFFECTS ON PESTICIDE DRIFT FROM AN IRRIGATED ORCHARD

Spray transects through an 11-m-tall pecan orchard with an air-blast orchard sprayer were replicated 10 times over a wide range of atmospheric stability conditions. Drift was measured by collecting tracer (malathion) using ground plates (f), high volume air samplers (hv), and string (s) collectors distributed downwind in the adjacent field out to a maximum distance of 18 canopy heights (198 m). Atmospheric conditions were measured above the orchard canopy with fast-response, three-dimensional wind, temperature, and humidity sensors. Atmospheric stability, characterized by the surface layer stability parameter ( ae), was the primary factor affecting drift amounts measured on and above the adjacent field. On average, the total amount of drift caught by the samplers in very stable conditions was 5.9, 3.6, and 2.1 times the amount of drift in unstable conditions for the plates, the hvs, and the strings, respectively. The transition from one condition to the other took place over a very small stability range where the air was dynamically stable (0.0 < ae< 0.3). In this range, very small changes in atmospheric conditions resulted in very large changes in the atmosphere’s aerosol transport characteristics. The effect of stability on the amount of drift collected in the adjacent field is described by a symmetric hyperbolic tangent function over the entire range of stability encountered.

Relative drift potential and droplet size spectra of aerially applied Propanil formulations

Wind tunnel studies were carried out using a Malvern (Malvern Instruments, Spring Lane South, Malvern, UK) laser particle size analyser to measure the droplet size spectra produced by an emulsifiable concentrate (EC), a water dispersable granule (WDG) and a liquid flowable (LF) formulation of Propanil with and without a non-ionic surfactant or a crop oil. The relative drift potential of each combination of formulation and adjuvant was determined in the field by measuring the relative recovery on vertical strings, placed 61 m downwind, for formulations sprayed simultaneously from a Cessna Ag Husky airplane, using a twin-tracer fluorescent dye technique. Differences were observed in the droplet size spectra and the relative drift potential of the three formulations and two adjuvants. Under the conditions of this study, there was a 25% difference in droplet size and a fivefold change in drift potential between the formulation types. The EC formulation produced the smallest vmd and the greatest amount of drift.

AIRBLAST SPRAY PARTITIONING IN A MATURE PECAN ORCHARD

Spray applications of Malathion were made with a radial airblast sprayer in an 11 m tall, mature pecan orchard, in the Middle Rio Grande valley of New Mexico. Measurements of drop size distributions from the sprayer were made with an imaging laser drop size measurement system. Sprayer effectiveness in penetration of the tree canopy was examined by sampling a vertical profile of droplet sizes on the opposite side of the row from the application. Spray volume samples were collected with continuous string samples arranged on a cross-row rectangle frame encompassing two tree rows. The first tree row reduced the overall Dv0.5 by a factor of 7. The measurements indicated that, overall, 4.5% of the total mass sprayed went out the top of the canopy; 22.2% was deposited on the ground between and beneath the adjacent tree rows; 12.2% passed through the left side tree row; and 4.0% passed through the right side tree row. The remainder, 57.1% of the material, was assumed captured by the adjacent tree rows.

Drift control polymers and formulation type affect volumetric droplet size spectra of propanil sprays

This study was conducted to investigate the effect of drift control adjuvants and formulation types on the volumetric droplet size spectra of simulated aerial sprays of propanil. Three polymer-based drift control adjuvants were evaluated with each of two formulations of the herbicide propanil in wind tunnel trials. An invert suspension oil used as a drift control agent was included in the trials. Each of the three polymer-based adjuvants significantly changed the volumetric droplet size spectrum of both the emulsifiable concentrate and the liquid flowable formulations. The invert suspension oil had no effect on the droplet size spectrum of either formulation. Volumetric droplet size distributions given by a laser particle sizer for propanil wind tunnel atomization data were studied using analysis of variance (ANOVA) and Kolmogorov-Smimoff (K-S) statistical tests. The ANOVA considered 6 distribution parameters (D 32 , D v0.1 , D v0.5 , D v0.9 , D 43 and relative span) while the K-S considered the entire distribution. The most frequent agreement was obtained for the K-S test and the ANOVA when considering D v0.5 , D v0.9 , and D 43

Polymer and invert emulsifying oil effects upon droplet size spectra of sprays

Abstract A series of wind tunnel atomization studies were carried out to investigate the effects of polymer and invert suspension oil “drift control adjuvants” upon the droplet size distribution spectra produced by nozzles typically used in aerial and ground based spraying of pesticides. A D8–46 disc and core was used as a typical aerial application nozzle, and an 8003 fan nozzle was used for the ground based sprayers simulation. The droplet size spectra were evaluated in a wind tunnel using a Malvern 2600 laser particle size analyzer immediately upon mixing and at 15 minutes after re‐circulation through a pumping system. The addition of the polymer‐based adjuvants significantly increased the droplet size spectra parameters of the spray cloud, but all the polymer products showed signs of breakdown of their molecular arrangements in the liquid medium, as a result of agitation. The invert suspension oil adjuvant did not change the droplet size spectra markedly, nor did it show signs of breakdown of the inte...

Droplet Size Spectra of Dipel™ Sprayed Through Different Atomizers

Droplet size spectra were measured for water and two aqueous flowable (AF) formulations of Bacillus thuringiensis sprayed from nozzles under simulated aerial application conditions. Spray deposit patterns on Kromekote cards were assessed in field trials using a Cessna AgHusky aircraft fitted with either 8004 nozzles or AU5000 atomizers. The spray liquids were tagged with a tracer dye for subsequent image analysis to determine droplet densities.

Deposition, distribution, persistence and fate of bacillus thuringiensis variety kurstaki (BTK) in pecan orchards following aerial and ground appucations to control pecan nut casebearer larvae

Abstract Aqueous mixtures of Bacillus thuringiensis Berliner var. kurstaki (Btk) were applied over three plots located in a pecan orchard in New Mexico, USA at a dosage rate of 39.6 billion international units (BIU)/ha and volume rates of 9.4 L/ha (Plot 1), 935 L/ha (Plot 2), and 47 L/ha (Plot 3). Plots 1 and 3 were sprayed aerially using a Cessna 188 aircraft fitted with Micronair AU 5000 atomizers and D8–46 disc‐core (hydraulic) nozzles, respectively. Plot 2 received ground application using a Wilbur‐Ellis air‐blast sprayer. Spray deposit patterns on artificial samplers and live pecan substrates were determined by quantifying the δ‐endotoxin at three different levels in the tree canopy and at ground level using enzyme‐linked immunosorbent assay (ELISA). Droplet density (droplets/cm2) and size spectra were also assessed to evaluate the uniformity of coverage at the three canopy levels using horizontal and cylindrical (vertical) Kromekote card samplers. Droplet density and size spectra on the Kromekote ca...

Quantifying the Amount of Aerial Spray in the Air Over Time for Vector Control Operations

The purpose of this project was to develop a technique to measure remotely, in real-time, aerosol mass remaining in the air at various times after spraying. Lidar measurements of plumes from a spray aircraft were combined with drop size distributions and spray rates to estimate the mass of material remaining in the air and drifting in real time. The spray aircraft was equipped with Micronair atomizers releasing very fine spray. The air was very stable and the spray plume was visible in the regions scanned by the lidar for up to 5 minutes.

Prediction of spray drift using insecticide tracers and two types of collector

Abstract Two insecticides, carbaryl and chlorpyrifos, were evaluated at low concentrations as tracers to predict the behaviour of spray clouds of malathion at field strength. Aerial sprays were produced from a Cessna Ag Husky equipped with a dual liquid dispersal system, spraying simultaneously. Spray drift was measured at 90 or 30 m downwind using 1.6 mm polyester cord and 0.6 mm monofilament line suspended from a helium‐filled blimp tethered 15.25 m above ground level. Recoveries of malathion averaged 87.3% and 85.2% of the amount predicted from the tracers on the monofilament and polyester, respectively. The coefficients of variation for 12 flights were 50.9% for the monofilament line, and 17.4% for the polyester cord.