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United States Department of Agriculture

Agricultural Research Service


Location: Application Technology Research Unit

2012 Annual Report

1a.Objectives (from AD-416):
Develop precision sprayers that can continuously match canopy characteristics to deliver agrichemicals and bio-products accurately to nursery and fruit crops. Identify and characterize factors that have the greatest impact on foliar pesticide spray application efficiency: determine how water droplets amended with spray additives, relative humidity and the morphological surfaces of leaves affect the droplet evaporation time, spread factor and residual pattern on leaves; determine how the droplet size and velocity, spray formulation, and morphological surface of leaves affect spray impact, retention and coverage. Identify and evaluate agrichemicals and bio-products that can be precisely delivered through drip irrigation systems.

1b.Approach (from AD-416):
Precision sprayers with wide range controllable flow rate, multi-jet nozzles will be developed to reduce the amount of pesticides required by matching spray characteristics to specific types of ornamental nursery and fruit trees. Fast response, high resolution, non-contact sensors will be used to detect the plant size, shape, density and position. Based on the plant structure data from the sensors, air velocity, spray application rate and number of jets will be determined to control the spray outputs as needed. All these operations will occur as the sprayer moves past the plant, providing uniform spray coverage with minimum off-target loss. Evaporation time, spread factor and chemical residual pattern area of individual droplets containing spray additives on leaves will be measured via sequential imaging under controlled conditions. Droplets will be placed inside an environmental-controlled chamber under a stereomicroscope and a high definition digital camera. A large database will then be developed including droplet evaporation time, and deposit pattern area on leaves with different surface characteristics, droplet sizes, chemical formulation components, and relative humidity conditions. A laboratory system will be developed to determine dynamic effects of spray characteristics on spray impact, retention and coverage on fine surface structure plants. All individual pesticide spray application variables will be controlled under laboratory conditions. The system contains a turntable, a mono-disperse droplet generator and uniform air carrier to deliver droplets onto leaves or selected polymer targets with defined surface properties. Droplet impact and rebound velocity will be measured with a particle/droplet laser image analysis system. A cold field emission scanning electron microscope (CFESEM) and a variable pressure scanning electron microscope will be used to determine leaf surface fine structure, droplet coverage area, residue deposit form and composition, and distribution of active ingredients on leaf target surfaces. Variables will be droplet size, droplet velocity, travel speed, type of liquid formulation, physical properties and concentration of spray additives, leaf orientation, leaf deformation, leaf wax and leaf roughness. Relationships among the spray droplet retention, distribution and coverage area on leaf surfaces with the variables will be determined and documented in a large database as a guideline to choose the optimum operational parameters. An engineering testing system for delivering agrochemicals and bio-pesticides through drip irrigation will be developed. All individual delivery variables will be controlled in the system. The distribution uniformity of agrochemicals and bio-pesticides with different physical properties and particle sizes throughout drip lines and in the soilless substrates and soil will be investigated. Tests will also include determination of emitter sizes and amounts of water needed to diffuse bio-pesticides in the soilless substrate in various size containers. A new injection unit will be developed to precisely deliver suspendable bio-pesticides through drip irrigation.

3.Progress Report:
An automatic flow rate control system with a new high speed laser sensor and pulse width modulation controlled solenoid valves was designed to manipulate the output of spray nozzles simultaneously to match tree structures. Multi-channel driver and protection circuits for activating solenoid valves were developed to modulate variable-rate outputs in real time. An embedded computer (PC/104) along with a touch screen was used to process control algorithms and to fulfill communications between the operator and the control system. Laboratory tests were conducted to verify the accuracy and reliability of the flow rate control system.

Air jet velocity distributions from the newly developed air assisted, five-port sprayer were measured at various locations in an open terrain and inside tree canopies. The air jet velocity was controlled by changing the sprayer fan inlet diameter and was measured with a constant temperature anemometer system coupled with hot-film sensors. Other variables for the tests were sprayer travel speed, tree canopy structure, horizontal and vertical distances from spray nozzles, and fan inlet diameter.

Spray deposition and coverage inside canopies of various structures were determined with different application rates and air jet velocities for the development of new variable-rate air-assisted sprayers.

Field efficacy tests were conducted to evaluate the control of aphids and powdery mildew by use of a newly developed ultrasonic sensor controlled variable-rate sprayer in a commercial nursery in Oregon. The control efficiency was also compared between the new variable-rate sprayer and a conventional constant-rate sprayer.

Biological surfactants were investigated to improve droplet behaviors on leaf surfaces. Droplet spread area and evaporation rate on various waxy and hairy leaf surfaces were measured with different concentrations of the biological surfactants, and were compared with conventional surfactants.

Dispersion and evaporation of single droplets amended with four different classes of spray adjuvants on four soybean plant surfaces were investigated. Tests were conducted under the controlled conditions to identify the best class of adjuvants and optimal concentrations to improve pesticide spray application efficiency for soybeans.

A system was developed to determine pheromone evaporation rates under controlled environmental conditions. The system was able to control ambient temperature and relative humidity separately. Weight changes of three commonly used pheromones were measured at various temperatures and relative humidities. Each sample was tested for seven days with the sampling rate of 15 minutes per weight measurement.

A system was developed to investigate droplet dynamic impact and retention on leaf surfaces. The system consisted of a uniform droplet generator, two high speed digital video cameras, a constant speed track, a leaf holder, and a cool light source. Dynamics of droplet impact, rebound and retention on two waxy leaves were determined with different droplet diameters, droplet discharge speeds, nozzle travel speeds, and leaf surface orientations.

1. Air velocity profiles of air-assisted five-port sprayer. Although current air-assisted sprayers provide improved spray penetration and deposition uniformity, they are not able to adjust both liquid and air flow rates as needed and thus spray losses are still considerable. Future variable-rate sprayers should have a capability to control both liquid and air flows to match tree canopy structures. This study investigated the effect of fan inlet diameters on characterization of air velocity profiles from an air-assisted five-port sprayer, in an effort to form a basis for the development of an automatic device to control the air flow rate for the future variable-rate sprayers. Test results demonstrated that the air velocities and airflow pressures for a particular fan inlet diameter were relatively uniform, confirming the capability of the sprayer to discharge uniform spray profiles for carrying droplets. Consequently, this study established a feasible and economic approach for the new precision sprayers to achieve the variable air rate function in orchard and nursery applications. With this function, sprayers will be able to control the amount of air flow as needed to prevent crops from either over sprayed or under sprayed, and to minimize excessive off-target losses to the air and ground from droplets passing through the canopy.

2. Development of variable-rate hydraulic boom sprayer for nursery liner applications. Pesticide application rates for ornamental nursery fields are determined by the largest tree group. Thus, over-applications of pesticides in ornamental nurseries are frequently observed due to tree size variations and no automated rate adjustment function in field sprayers. An experimental sprayer, which autonomously detects nursery tree canopy and its size and adjusts spray output in real time, was developed to address the pesticide over-application in ornamental nursery fields. The sprayer was tested to determine sprayer’s accuracy in spray timing. In addition, reliability in detecting canopy and ground speed effects in spray deposit and coverage were investigated in a laboratory test field. The results from this study demonstrated the newly developed sprayer was able to deliver uniform spray deposition and coverage for nursery liner applications despite variations in liner canopy size and sprayer travel speed. The new variable-rate sprayer would be beneficial to growers in terms of reducing pesticide cost and off-target loss with the capability of adjusting spray outputs automatically to match tree sizes.

3. Evaluation of a newly developed variable-rate sprayer for nursery liner applications. Properly applying chemicals to nursery liner crops is essential to protect them from biological harm and maintain their quality. However, few application technologies have been specifically designed for these crops and nursery growers have to use either orchard or modified ground sprayers for their chemical applications. An experimental variable-rate sprayer was designed and tested for liner applications in a laboratory plot. Its spray deposit, coverage, and droplet density inside canopies of various nursery liner varieties was compared with constant-rate applications. The variable-rate application had lower variation in spray deposits inside tree canopies than constant-rate applications. Moreover, spray volume savings of the variable-rate sprayer were up to 71% compared to the conventional application of the constant rate that was normally recommended for liner spray applications. Therefore, the newly developed variable-rate sprayer would bring great reductions in pesticide use and safeguard the environment for the nursery liner production.

4. Development of variable-rate air-assisted sprayer. In nurseries and orchards, foliar pesticide application is the most effective method to protect crops from pest damages and prevent yield losses. However, due to a great diversity in canopy structure and foliage density, conventional spray systems and methodologies are inefficient and often cause excessive pesticide usage. This research developed an experimental air-assisted variable-rate spraying system with integration of high-speed laser scanning technology to characterize the occurrence, height, width and foliage density of tree canopies and then control spray outputs to match targeted tree structures. The accuracy of the variable-rate sprayer to deliver chemicals to targets was validated by examining the uniformity of spray coverage inside different ornamental trees at different travel speeds. Test results demonstrated that the sprayer had capabilities to achieve variable spray rates for different canopy volumes and foliage densities with acceptable variations in spray coverage inside tree canopies. Now, it is feasible to have a new generation of precision sprayers for nursery and orchard growers to prevent excessive pesticide use, and thus reduce production costs, worker exposure to pesticide risks, and adverse environmental contamination.

5. Dispersion and evaporation of droplets amended with adjuvants on soybeans. Soybeans are often susceptible to insect infestations and to diseases that cause significant yield losses. Protective pesticide spray applications on soybeans can increase yield and quality, but they also increase production costs which can be ameliorated with less spray mixtures and minimized off-target loss. The effects of four different groups of adjuvants at various concentrations on dispersion and evaporation of single droplets were investigated under controlled conditions. This systematic investigation precisely demonstrated that adjuvant-amended foliar sprays increased the coverage area on soybean plants by over 400%, which is a fourfold reduction in spray volume. The use of adjuvants also improved the homogeneity of sprayed pesticides. These findings provide convincing evidence to growers that they can potentially reduce significant amounts of spray mixtures by using adjuvants to increase droplet dispersion on soybean plants, resulting in reduced soybean production cost and also reduced environmental contamination.

Review Publications
Jeon, H., Zhu, H. 2012. Development of variable-rate sprayer for nursery liner applications. Transactions of the ASABE. 55(1):303-312.

Jeon, H., Zhu, H., Derksen, R.C., Ozkan, E., Krause, C.R. 2012. Performance evaluation of a newly developed variable rate sprayer for nursery liner applications. Transactions of the ASABE. 54(6):1997-2007.

Gu, J., Zhu, H., Ding, W., Jeon, H. 2011. Droplet size distributions of adjuvant-amended sprays from an air-assisted five-port PWM nozzle. Atomization and Sprays. 21(3):263-274.

Zhu, H., Zondag, R.H., Krause, C.R., Merrick, J., Daley, J. 2011. Reduced use of pesticides for effective controls of arthropod pests and plant diseases. Journal of Environmental Horticulture. 29(3):143-151.

Last Modified: 4/17/2014
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