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United States Department of Agriculture

Agricultural Research Service


Location: Application Technology Research Unit

2010 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

Leaf locations included the interveinal area, midrib and secondary vein on both adaxial and abaxial surfaces. Tests were conducted with 300 and 600 µm droplets containing water and a nonionic surfactant. The ambient temperature was 25ºC and relative humidity was 60. The wetted area was significantly larger on the adaxial area than on the abaxial surface but the evaporation time between both surfaces was not significantly different. For the whole leaf, the average evaporation time of 300 µm droplets was decreased by 44% and the average wetted area was increased by 202% when 0.25% nonionic surfactant was added into the spray solution. The total mean evaporation time increased 279% and the wetted area increased 166% without the surfactant, 452% and 229% with the surfactant when the droplet diameter increased from 300 to 600 µm. The 300 µm droplets had longer evaporation time per droplet volume and greater wetted area per droplet volume than the 600 µm droplets, thereby promoting the notion that increased pesticide application efficiency could be achieved by smaller droplets. This study also demonstrated that the ratio between spray coverage area and the amount of sprays required could be greatly increased by using surfactants, greatly reducing spray application rates and increased application efficiency. After deposition and evaporation, residue patterns of 500 µm sessile droplets that incorporated four classes of adjuvants on five different waxy plants were investigated. Adjuvants tested were two types of oil-based Crop Oil Concentrate (COC) and Modified Vegetable Oil (MVO), a Nonionic Surfactant (NIS), and a type of mixture Oil Surfactant Blend (OSB). Water-only droplets were also tested for comparative purposes. The water-only droplets did not spread at all and formed extremely small wetted areas on the leaf surface. The addition of an adjuvant to the spray solution significantly reduced the contact angle and increased the wetted area, but the improvements varied with the plant species and the adjuvant class. In general, the MVO and NIS enhanced the droplet spread and maintained the droplet evaporation time on the waxy leaf surfaces. After evaporation, the residues formed patterns of “coffee rings”. Droplets with oil-based adjuvants had more uniform residual distribution in the deposition patterns than droplets with the surfactant adjuvant. 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. Droplet size distributions from spray nozzles were measured. Laboratory and field tests were conducted to verify the accuracy of spray controller timing and modulation. A precision air-assisted sprayer implementing an automatic variable rate control system is in the process of development for ornamental nurseries and fruit trees. Cooperator’s Designated Representatives directly worked with the ADODR to plan and execute the project. They met daily to discuss the project progress.

Last Modified: 4/23/2014
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