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United States Department of Agriculture

Agricultural Research Service


Location: Application Technology Research Unit

2009 Annual Report

1a.Objectives (from AD-416)
Objective 1: Investigate how droplet impact, retention, and evaporation are affected by target surface characteristics and pesticide formulation physical properties and establish a complex pesticide transfer function from fundamental research to new precision sprayer development. Objective 2: Develop computer control systems for laser-guided precision sprayers to accommodate various tree canopy characteristics.

1b.Approach (from AD-416)
In cooperation with the ARS Application Technology Research Unit, Wooster, OH, perform the following: (1) determine evaporation time, spread factor and chemical residual pattern formation of droplets containing spray additives on horticultural leaves via sequential imaging under controlled conditions; (2) investigate influences of droplet size and velocity, spray formulation, and morphological surface of leaves on spray droplet impaction, retention and coverage to develop strategies for enhancing delivery to target areas; and (3) develop a precision air-assisted sprayer with multi-jet nozzles to reduce the amount of pesticides required by matching spray characteristics to specific types of nursery and fruit trees. A fast response, high resolution controller will be developed to control air velocity, spray application rate and number of jets required for each air jet nozzle. All these operations will occur as the sprayer moves past the tree, providing uniform spray coverage of the tree with minimum off-target loss beyond the tree row.

3.Progress Report

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 sizing from 246 to 886 microns at relative humidity (RH) ranging from 30 to 90% were measured with sequential images under controlled laboratory conditions. Droplets were placed inside an environmental-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 insecticides. The droplet evaporation was investigated on the surfaces of crabapple leaf surfaces, hydrophilic and hydrophobic glass slide surfaces, respectively. Adding surfactant into spray mixtures greatly increased droplet coverage area on the surfaces while droplet evaporation time was greatly reduced. For a 343 micron droplet on the crabapple leaf at 60% RH, the evaporation time decreased from 70 to 50 seconds and the maximal coverage area increased from 0.366 to 0.890 mm2 after the surfactant was added into the spray mixture containing water and insecticide. Adding the drift retardant into spray mixture slightly increased the droplet evaporation time and decreased the droplet coverage area. Also, 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 could increase 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.

A high speed laser scanner was investigated to detect gaps between trees, and measure tree characteristics. Interfaced program between laser and computer was developed to determine the tree size and shape.

Cooperator’s Designated Representative directly worked with the ADODR to plan and execute the project. They met daily to discuss the project progress.

Last Modified: 4/19/2014
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