Roy D Sweeb

Spray Deposition and Mass Balance in Citrus Orchard Applications

A sampling system was used to quantify on-canopy spray deposition and off-target losses from five air-carrier sprayers commonly used in citrus spray applications. The samplers consisted of continuous loops of cotton ribbon that were stretched out above the tree canopies, on the tree sides, and above the orchard floor. The loops extended to the third rows on each side of the spray course. The sprayers had different design configurations, and their airflow rates, nozzle selections, droplet size spectra, and operating parameters varied markedly. Spray solutions containing a fluorescent tracer were applied between two tree rows, the targets were collected in small segments, and spray deposition on various sample sections was quantified by fluorometry. The study was conducted in five replications. Overall, there was no significant difference in canopy deposition of the sprayers, and spray deposition on tree rows adjacent to the sprayer accounted for 73.0 - 79.4% of the total sprayer output. Cumulative deposition of three rows on both sides of the sprayers ranged from 74.3 to 82.1%, and the off-target losses (ground deposit plus spray drift) amounted to 17.9 - 25.7%. Comparing ground deposits or drift estimates alone, there were significant differences among the five sprayers. Ground deposits ranged from 8.7 to 19.6%, and drift estimates were mostly in the 6.1 - 14.0% range.

Comparison of string and ribbon samplers in orchard spray applications

The main objective of this study was to establish the relationship between spray deposition on ribbon and string samplers in field applications. The experiment involved five commonly used citrus air-carrier sprayers, which included both conventional and tower configurations, equipped with axial- or cross-flow fans and hydraulic nozzles or rotary atomizers. A sampling structure, consisting of vertical and horizontal lines of polyester string and cotton ribbon, was constructed in a citrus grove. Spray mixtures, containing a fluorescent tracer, were applied at different volume rates and ground speeds (nine treatments) on a 30 m course between two tree rows. Shortly after spraying each replication, the lines were collected in pieces. In the laboratory, the amount of deposit was determined by fluorometry. Weather data recorded during the applications were used as co-variables in the analysis of variance. Each treatment was replicated 3 to 5 times. The results showed a significant difference between capture efficiencies of the two target types. In all sample locations, the amount of spray deposit on the string was higher than that captured on cotton ribbon. Overall, the mean and standard deviation of the string/ribbon deposit ratios were 2.3 and 0.7, respectively.

Regulating Airflow of Orchard Airblast Sprayer Based on Tree Foliage Density

Adjustment of orchard sprayer air output, using an electro-mechanical system, was investigated for reducing spray losses. This system automated horizontal movement of an air deflector plate inside the sprayer air outlet by using foliage density signals from a laser scanner. A field test was conducted to evaluate the role of the deflector plate position in modifying air penetration through tree canopies of different foliage densities. Another test involved sampling horizontal movement of spray droplets, in an open area within a citrus orchard, at different deflector plate positions. The deflector plate could move from the innermost to the outermost position (to change horizontal airflow from 7.6 to 1.9 m3 s-1) in about 3 s. Various plate settings showed differences in air penetration across tree canopies with various foliage densities. The deflector plate also had an effect on the spatial movement of droplets to some extent. The results suggest that limiting the sprayer airflow to the canopy depth may potentially reduce spray losses from orchard applications.

Mass Balance of Citrus Spray Applications

A sampling system was used to quantify on-canopy spray deposition and off-target losses from five air-carrier sprayers commonly used in citrus applications. The samplers consisted of continuous lines (loops) of cotton ribbon that stretched out above tree canopies, on tree sides, and above orchard floor. They extended to the third rows on each side of the application line. The sprayers had different design configurations and their airflow rates, nozzle selections, droplet size spectra, and operating parameters varied markedly. Spray solutions containing a fluorescent tracer were applied between two tree rows, the targets were collected in small segments, and spray deposition on various sample sections was quantified by fluorometry. The study was conducted in five replications.

Solar and Storage Degradations of Oil- and Water-Soluble Fluorescent Dyes

The assessment of spray deposit efficiency is an important aspect in pesticide application technology research. Since fluorescent tracer dyes serve as useful markers for evaluating spray deposits in many spray application investigations, it is necessary to study the stability and degradation of the fluorescent deposits during storage and exposure to solar radiation before using them under field conditions. Therefore, this study was carried out to evaluate the degradation characteristics of spray deposits prepared with two fluorescent dyes (oil-soluble Yellow 131SC®, and water-soluble Pyranine 10G®), due to the solar radiation and duration of sample storage.

Adjusting Airblast Sprayer Airflow Based on Tree Foliage Density

This paper reports on the development of an electro-mechanical system for exploring the idea of adjusting air output from an airblast sprayer to reduce spray losses from orchard applications. A moving air deflector plate was designed and its horizontal motion was automated by integrating a motion control system consisting of a stepper motor, controller, GPS receiver, laptop computer, and a laser scanner. Foliage density estimates from the laser scanner were used to actuate the mechanical components. Also, two experiments were conducted to evaluate the utility of the system in real-time changing of air output. The first experiment evaluated the role of deflector plate position in modifying air penetration characteristics across trees of different foliage densities. The second experiment consisted of sampling spatial movement of spray droplets with five deflector plate positions. In field trials, the deflector plate moved from the innermost to outermost position (based on foliage density) to change horizontal airflow from 7.6 to 1.9 m3/s, respectively, in 3 s. Various plate settings showed differences in air penetration across tree canopies with various foliage densities. The deflector plate also had an effect on the spatial movements of droplets to some extent. A change of plate setting from innermost (maximum air) to outermost (minimum air) showed about 37% reduction in mean deposition at Far sample location, at high application rate. The results indicate the change in air volume could facilitate reducing off-target spraying in orchard applications.

Degradation of Oil- and Water-Soluble Fluorescent Dyes

The assessment of spray deposit efficiency is an important aspect in pesticide application technology research. Since fluorescent tracer dyes serve as useful markers for evaluating spray deposits in many spray application investigations, it is necessary to study the stability and degradation of the fluorescent deposits during storage and exposure to solar radiation before using them under field conditions. Therefore, this study was carried out to evaluate the degradation characteristics of spray deposits prepared with two fluorescent dyes (oil-soluble Yellow 131SC®, and water-soluble Pyranine 10G®), due to the solar radiation and duration of sample storage.

Spray Capture Efficiencies of Ribbon and String Targets Used in Orchard Applications

The main objective of the study was to establish the relationship between spray deposition on ribbon and string samplers in filed applications. The experiment involved five commonly used citrus air-carrier sprayers, which included both conventional and tower configurations, equipped with axial- or cross-flow fans and hydraulic nozzles or rotary atomizers. A sampling structure, consisting of vertical and horizontal lines of polyester string and cotton ribbon, was constructed in a citrus grove. Spray mixtures, containing a fluorescent tracer, were applied at different volume rates and ground speeds (nine treatments) on a 30-m course between two tree rows. Shortly after spraying each replication, the lines were collected in pieces. In the laboratory, the amount of deposit was determined by fluorometry. Weather data recorded during the applications were used as covariables in the analysis of variance. Each treatment was replicated 3-5 times. The results showed a significant difference between capture efficiencies of the two target types. In all sample locations, the amount of spray deposit on the string was higher than that captured on cotton ribbon. Overall, the mean and standard deviation of the string/ribbon deposit ratios were 2.3±0.7.