Laser-guided variable-rate air-assisted sprayer for ornamental nursery and orchard applications

Transcription

1 Ref: C0093 Laser-guided variable-rate air-assisted sprayer for ornamental nursery and orchard applications Heping Zhu 1, Yu Chen 1,2, Hui Liu 1,2, Yue Shen 1,2, Jiabing Gu 1,5, Erdal Ozkan 2, Richard Derksen 1, Mike Reding 1, Chris Ranger 1, Luis Canas 2, Charles Krause 1, Jim Locke 1, Stan Ernst 2, Randy Zondag 2, Amy Fulcher 3, Robin Rosetta 4 1 USDA-ARS Application Technology Research Unit, 1680 Madison Avenue, Wooster, OH 44691; 2 The Ohio State University; 3 University of Tennessee; 4 Oregon State University; 5 Nanjing Agricultural University. Heping.Zhu@ars.usda.gov Abstract Critical innovative technology is needed to increase application efficiencies and reduce uncertainties for conventional pesticide sprayers to achieve real cost benefits with new pesticide application strategies for tree crop producers, consumers and the environment. A precision air-assisted sprayer was developed to apply appropriate variable amounts of pesticides for orchard and ornamental nursery applications. The sprayer integrated a highspeed laser scanning sensor, a custom-designed signal processing program, an automatic flow controller, pulse-width-modulated variable-rate nozzles and a multi-port air-assisted delivery system. The accuracy and consistency of the sprayer to assess tree canopy structures and the effects of sprayer travel speeds and canopy structures on the uniformity of spray deposition and coverage inside canopies were evaluated with multiple target species in three commercial nurseries and an orchard. The spray quality inside canopies and off-target losses were compared with conventional constant-rate applications. Pest control efficacy of the sprayer was also tested in commercial nurseries in three different states. Laboratory and field tests demonstrated that the laser-guided variable-rate sprayer had the capability to automatically control spray outputs of individual nozzles to match canopy characteristics and occurrence in real time. With comparable pest control efficacies during a growing season, the laser-guided sprayer reduced pesticide use by 46% to 68%, airborne spray drift by up to 70% to 100%, and spray loss to the ground and through the space between trees by 71% to 85%. Therefore, this new generation of precision sprayers will prevent excessive pesticide use and reduce production costs, worker exposure to pesticide risks, and adverse environmental contamination. Keywords: automation, precision sprayer, spray deposition, spray drift, tree crop 1. Introduction Current application technology for floral, nursery, and tree fruit crops requires excessive amounts of sprays to control pests due to a great diversity in canopy structure and density (Zhu et al., 2011a). Precision pesticide application equipment and strategies are needed to reduce pesticide usage. One way to meet this need is to use sensor technologies to identify target trees and then apply the precise amount of materials needed for adequate insect and disease control. Proceedings International Conference of Agricultural Engineering, Zurich, /7

2 Variable air-assisted sprayers that apply sprays based on tree occurrence, structure and foliage density are needed to overcome the disadvantages of conventional air-assisted sprayers (Fox et al., 2008). Variable-rate flow control systems integrated with ultrasonic sensors have been developed to retrofit to conventional sprayers (Giles et al., 1989; Solanelles et al., 2006; Jeon and Zhu, 2012). However, the accuracy of ultrasonic sensors to detect tree canopies is limited by detection distance, temperature, humidity, and ground speed (Jeon et al., 2011). They do not have the capability for continuous three-dimensional measurements because they have large divergence angles and low measurement resolution and consequently can only be used for point measurements. The laser scanning technology due to its high accuracy has great potential in the development of precision spraying systems for tree crop applications (Chen et al., 2012; Wei and Salyani, 2004, 2005; Palacin et al., 2007, 2008). The accuracy of laser sensors is stable and independent of the environment. When they are mounted on a moving platform, their measurements of plant canopies can be converted to three-dimensional profiles (Rosell et al., 2009a, 2009b; Chen et al., 2012). The objective of this research was to develop a precision air-assisted variable-rate spraying system with integrated laser scanning technology to characterize the occurrence, height, width, and foliage density of a tree canopy and then control spray outputs to match the target tree structures. 2. Materials and methods A unique variable-rate, air-assisted precision sprayer was developed to visualize the presence, size, shape, and foliage density of target trees and apply only the necessary amount of pesticide in real time (Fig. 1). The precision processing system of this sprayer is an integration of a high-speed, 270 radial and 30-m range laser scanning sensor in conjunction with a non-contact Doppler radar travel speed sensor, an automatic nozzle flow rate controller, an embedded computer, a touch screen, a manual switch box, and four fiveport nozzle manifolds on each side of the sprayer. Figure 1: Prototype of the newly-developed laser-guided air-assisted variable-rate sprayer. Proceedings International Conference of Agricultural Engineering, Zurich, /7

3 The base of the air and liquid delivery system in the laser-guided variable-rate sprayer mainly consists of an axial turbine fan, a 400 L spray tank, and a diaphragm pump from a conventional vineyard sprayer (Hardi International A/S, Taastrup, Denmark). Each five-port nozzle manifold incorporates five modified flat-fan pattern nozzles, and each nozzle is coupled with a 10-Hz pulse width modulation (PWM) controlled solenoid valve. The nozzle flow rate is controlled by modulating the 10-Hz pulse width (or duty cycle) of the solenoid valve. All 40 nozzles on the 8 manifolds on two sides of the sprayer independently discharge variable flow rates to their designated canopy sections on their respective sides. During spray applications, the sprayer is mounted on a tractor with a standard three-point hitch, and the tractor PTO driven system powers the spray pump and air fan. The four air-assisted fiveport nozzles at each side are arranged as a tower sprayer nozzle configuration and each nozzle discharges sprays in a radial pattern. Hence, this sprayer has the advantages of conventional tower sprayers and air blast sprayers with additional automatic liquid variablerate function. Nozzles from the sprayer also provide relatively uniform droplet sizes and uniform air profiles (Gu et al., 2012). The laser scanning sensor is mounted between the tractor and sprayer to detect the return distance signals from the bilateral tree structure. Its accuracy was verified with regular-shape objects, artificial trees and field trees. The embedded computer is loaded with a dedicated C++ language algorithm developed to process the signals and translate them into tree surface structures. The algorithm also determines the presence of a tree canopy, and calculates its height, width, foliage density and volume. It then converts tree sectional canopy structure and sprayer travel speed into the requisite amount of sprays for each PWM controlled nozzle for each respective canopy section. Consequently, application rates of each nozzle are predetermined by its assigned sectional canopy structure. The laser sensor accuracy to detect tree canopy profiles was evaluated and compared with tree images taken from a digital camera. The flow rate controller is a compact design with an integration of multi-channel drivers and protection circuits along with two microprocessors for activating PWM solenoid valves (Liu et al., 2014). The two microprocessors generate flow rate commands to independently control flow rates of 40 nozzles simultaneously, which allows each nozzle output to be controlled automatically based on tree canopy structure and sprayer travel speed in real time. The controller is housed in a control box and connected to the embedded computer by a wire harness with pluggable connectors. The control box is mounted under the spray tank. The embedded computer was used because of its resistance to vibration, wide range of operating temperatures, and compact size. This capability allows variable-rate sprayers to be reliable and user-friendly under field conditions. The travel speed sensor is mounted at the bottom of the sprayer to acquire real-time ground travel speeds. The embedded computer, touch screen and switch box are mounted in the tractor cab (Fig. 2). The touch screen displays the sprayer travel speed, total spray volume discharged and spray width covered on each spray side, and individual nozzles that are active simultaneously. The operators can modify spray parameters on the touch screen as needed. The switch box contains three 3-way toggle switches that control the sprayer output from one or both sides in manual or automatic control mode. Figure 2: Embedded computer and touch screen in the tractor cab. Proceedings International Conference of Agricultural Engineering, Zurich, /7

4 The touch screen and switch box enable the communications between sprayer operators and the flow controller. All electronic devices are powered by a 12 VDC tractor battery. Additionally, a 10x6x2 cm rechargeable battery is wired to provide backup power in case of a power failure or a surge when starting the tractor. Another precaution includes a flat jet mounted on the top of the laser sensor that provides an air stream from the sprayer fan to prevent dust and droplet contaminations landing on the laser scanning sensor surface. After the laser-guided sprayer was designed, its capabilities to automatically match spray outputs to canopy structures and travel speeds was tested with different canopy structures, tree planting patterns and travel speeds in a laboratory plot, three commercial nursery fields, and a vineyard. The sprayer performance was also evaluated in an apple orchard by quantifying spray deposition inside canopies at leafing, half-foliage, and full-foliage growth stages, and was compared with conventional spray applications. Spray deposition uniformity inside canopies, off-target losses to the ground, around trees, beyond trees and in the air were measured at the three growth stages. Artificial nylon screen targets were used to collect spray deposits. A non-degradable fluorescent tracer (Brilliant Sulfaflavine) was mixed with spray solution for quantifying the amount of spray deposits on the target screens with a fluorescence spectrophotometer. Water sensitive papers were used to determine the spray coverage quality inside canopies with a scanning image program (Zhu et al., 2011). Biological control efficiency tests were also conducted in three ornamental nursery farms to control aphids and powdery mildew with the laser-guided sprayer and conventional airassisted sprayers. 3. Results and Discussion The laser sensor accuracy test demonstrated that the sensor along with the algorithm developed to translate the sensor signals into tree surface structures had the capability to measure canopy sizes for different shapes of trees accurately. For example, the similarity of paired canopy profiles of an apple tree at leafing and full-foliage stages taken from the laser sensor and the camera was greater than 0.90 (Fig. 3). The sensor and the algorithm were also able to estimate the foliage densities at different tree growth stages (Figs. 3a and 3b). There were no significant differences in the amounts of spray deposits (Fig. 4a) and spray coverage (Fig. 4b) inside tree canopies at different travel speeds between the laser-guided variable-rate sprayer and the conventional constantrate sprayer. Also, changing the travel speed in the range from 3.2 to 8.0 km h -1 did not significantly influence the spray deposition quality. These experiments also illustrated that the laser-guided sprayer, compared to conventional (a) From camera (b) From laser sensor Figure 3: Paired tree images taken with camera and laser sensor at two growth stages: (a) leafing, (b) full foliage. sprayers, reduced variations in spray deposition due to changes in tree structures and increased consistency of spray deposition uniformity on targets at different growth stages. Proceedings International Conference of Agricultural Engineering, Zurich, /7

5 (a) Spray deposits (b) Spray coverage Figure 4: Comparison of (a) the amonuts of spray deposits and (b) spray coverage inside 6 tree canopies at different travel speeds between the laser-guided variable-rate sprayer and the conventional constant-rate sprayer in an ornamental nursery field. On the other hand, compared to the constant-rate sprayers, the laser-guided variable-rate sprayer greatly reduced spray losses to the ground and in the air (Fig. 5) while their spray deposition quality inside the canopy was comparable. For example, reductions in the amount of spray losses to the ground and through the space between trees by the laser-guided sprayer were 85%, 80%, and 71% when compared with the conventional air-assisted sprayer at the leafing, half-foliage, and full-foliage growth stages, respectively (Fig. 5a). Similarly, the laser-guided sprayer reduced downwind airborne drift by 70%, 100%, and 90% at 5, 15, and 35 m downwind at the half-foliage stage, and by 87% and 100% at 15 and 35 m downwind at the full-foliage stage (Fig. 5b) (Chen et al., 2013). (a) Spray losses to the gound and around tree (b) Airborne spray drift Figure 5: Comparison of (a) spray off-target losses to the ground and around tree and (b) airborne spray drift in three growth stages between the laser-guided variable-rate sprayer and a conventional constant-rate sprayer in an orchard. Field biological control tests demonstrated that the laser-guided variable-rate sprayer had comparable insect control efficiencies and lower disease infection rates than the conventional air-blast sprayers (Fig. 6). For example, there were no significant differences in number of leafhoppers on red maple foliage between the laser-guided sprayer and conventional airblast sprayer treatments (Fig. 6a). However, there were lower powdery mildew infections on Norway maple trees with the laser-guided sprayer treatment than that with the conventional sprayer treatment (Fig. 6b). This was because the laser-guided sprayer produced the spray Proceedings International Conference of Agricultural Engineering, Zurich, /7

6 deposition distribution with lower variations across the tree height than the conventional sprayer with radial spray patterns. (a) Leafhopper infestation (b) Powdery mildew infection Figure 6: Comparisons of (a) leafhopper infestations on red maple trees and (b) powdery mildew infections on Norway maple trees between the laser-guided variable-rate and conventional air-blast sprayer treatments. With the comparable insect control efficiency and better disease controls or prevention, the average application rates during the growing season with the laser-guided sprayer were 412 L ha -1 in farm #1, 206 L ha -1 in farm #2 and 309 L ha -1 in farm #3 while the average application rates from the conventional constant-rate sprayers were 767, 514, 973 L ha -1, respectively (Fig. 7). The laser-guided sprayer reduced pesticide use by 46% to 68%. 4. Conclusions Controlled spray outputs to match canopy structures including foliage density in real time are now realistic with the newlydeveloped laser-guided variable-rate sprayer capabilities. Field tests demonstrated that the laser-guided sprayer reduced average pesticide use by 46% to 68% while pest control efficacies were comparable or better than conventional applications. Therefore, this new generation of precision sprayers significantly advanced the variable-rate pesticide spray technology, prevented excessive pesticide use, increased application efficiencies, reduced uncertainties for current pesticide sprayers, and was anticipated for benefits in profitability, worker safety and environmental improvements. 5. Acknowledgements Figure 7: Comparison of average spray application rates during a growing season between the laser-guided variable-rate and conventional airblast sprayer treatments in three farms. The authors acknowledge invaluable technical assistance from Adam Clark, Barry Nudd, and Keith Williams. We are also grateful to the USDA-NIFA Specialty Crop Research Initiative (Grant No ). Proceedings International Conference of Agricultural Engineering, Zurich, /7

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