Unmanned aerial application systems (UAAS) have recently gained momentum for the application of crop protection (CP) products. Due to their high operational efficiency, mobility, and low cost, UAAS may be perceived as a more viable option for spray application when compared to conventional application techniques, especially backpack/knapsack sprayers. However, being a relatively new technology and not a common practice in the USA, there are no best management practices or guidelines for testing UAAS spray performance. Therefore, this study was undertaken to assess the impact of different attributes pertinent to UAAS flight (e.g., altitude, speed, etc.), application (e.g., droplet size, tank additive, etc.), and UAAS design (e.g., nozzle placement relative to a the rotor) on spray performance. The spray performance was evaluated in terms of swath and spray drift (ground and airborne) using water-sensitive papers (WSP) and mylar card/string samplers, respectively. The samplers were respectively analyzed using image processing and fluorometry techniques. The different treatments under study were UAAS type (MG-1P and AG V6A+), flight altitude (1.5, 2.5, and 4.0 m) and speed (2 and 3 ms⁻¹), and nozzle type (XR11001 and XR8002 flat fan nozzles) with different droplet volume median diameter (VMD) at ~207 kPa (very fine [140 µm] and fine [196 µm], respectively). The results indicated a highly variable swath for both platform types. While nozzles under each rotor may be a common design in commercial UAAS, the results indicated that placement of nozzles out on a boom might have a less variable swath and a lower drift potential. In addition, flying slower, using a relatively larger droplet VMD (i.e., 196 µm at ~207 kPa) may reduce both ground and airborne drift. This study may serve as a guideline for growers/operators to evaluate their UAAS platforms and optimize key attributes pertinent to UAAS operation for effective spraying.

A solid set canopy delivery system (SSCDS) has the potential to be an efficient spraying technique because it minimizes chemical drift and allows timely spray applications even under adverse field conditions. A conventional SSCDS, working as a hydraulic spraying system, is controlled manually. Such operation makes it labor and time intensive for spray application in larger orchards. Therefore, a new hardware and software design was implemented in this project for field-level automation of a conventional SSCDS. An electronic control system (ECS) and a spray control unit (SCU) were developed and integrated with an improvised conventional SSCDS. A graphical user interface (GUI) was developed to provide user inputs to the ECS for valve actuation-based decision making. The SCU consisted of a microcontroller, a relay board, and a radio frequency (RF) module assisting in actuation of the solenoid valves in the desired sequence with commands from the ECS. Integrated RF trans-receiver modules facilitated closed-loop wireless communication between the ECS and SCU. This technical note elaborates on the successful integration of the hardware and software to achieve SSCDS automation and functionality, as well as the performance evaluation in a vineyard. The results confirmed the envisioned triggering sequence and solenoid valve actuation for different operating stages of the SSCDS over 120 m loop length. Moreover, the automated SSCDS had no significant differences in spray volume or pressure along the loop up to 82 m. Overall, the proposed integration will aid in automating SSCDS-based spray operation for larger orchards. To validate such a setup, further studies are planned for a centrally located control station and spraying several adjacent plots at a time. Keywords: Agricultural automation, Electronic control system, Precision spray application, Solid set canopy delivery, Spray control unit, Wireless communication.

Optimally configured solid set canopy delivery systems (SSCDS) can provide adequate spray performance in high-density apple orchards with a minimized risk of off-target pesticide drift. SSCDS configured in a shower-down emitter arrangement have been reported to be the simplest and most economical system. However, existing off-the-shelf emitters used in shower-down configurations have resulted in minimal deposition in lower canopy zones. Therefore, this study was focused on the modifications of off-the-shelf emitters to obtain a desirable spray pattern for adequate spray deposition in all the canopy zones. The modifications include redesigning the impact plate of two existing micro-emitters. Field tests were conducted to evaluate the spray performance of SSCDS with the non-modified emitters (treatment: SD1 and SD3) and contrast the results with modified emitters (treatment: SD2 and SD4). While the treatments SD1 and SD3 had off-the-shelf emitters with swivel plate and static spreader, respectively, the treatment SD2 and SD4 had similar emitters with modified impactor plates. In each treatment block, the apple canopy was divided into six zones and sprayed with a 500 ppm fluorescent tracer solution. Mylar cards and water-sensitive paper samplers were placed on the adaxial and abaxial leaf surfaces in each canopy zone to quantify spray deposition and coverage, respectively. The SSCDS treatments retrofitted with modified emitters, i.e., SD2 and SD4, were observed to have uniform and numerically higher deposition and coverage compared to SD1 and SD3. The SSCDS treatment with modified static spreader (i.e., SD4) resulted in the highest overall spray deposition (1405.7 ± 156.4 ng cm⁻² [mean ± standard error]) with improved mid (1121.6 ± 186.9 ng cm⁻²) and bottom (895.6 ± 149.3 ng cm⁻²) canopy deposition. Overall, the proposed emitter modification assisted in improved SSCDS spray performances and may be a way forward toward large-scale emplacements of such systems.

Solid Set Canopy Delivery Systems (SSCDS) are fixed agrochemical delivery systems composed of a network of micro-sprayers/nozzles distributed in perennial crop canopies. A previous SSCDS design composed of a 3-tier configuration using hollow cone sprayer nozzles has been shown to provide excellent coverage and deposition in high-density apple orchards. However, the hollow cone nozzles substantially increases the initial system installation costs. This study evaluated the effect of irrigation micro-emitters replacement on spray deposition, coverage and off-target drift. A micro-emitter used in greenhouse irrigation systems was duly modified to enhance its applicability with SSCDS. After laboratory assessment and optimization of the micro-emitters, a replicated field study was conducted to compare 3-tier SSCDS configured with either of modified irrigation micro-emitters or traditional hollow cone nozzles. Canopy deposition and off target drift were evaluated using a 500 ppm fluorescent tracer solution sprayed by the field installed systems and captured on mylar collectors. Spray coverage was evaluated using water sensitive papers. The overall canopy deposition and coverage for treatment configured with modified irrigation micro-emitters (955.5 ± 153.9 [mean ± standard error of mean] ng cm⁻² and 22.7 ± 2.6%, respectively) were numerically higher than the hollow cone nozzles (746.2 ± 104.7 ng cm⁻² and 19.0 ± 2.8%, respectively). Moreover, modified irrigation micro-emitter SSCDS had improved spray uniformity in the canopy foliage and on either side of leaf surfaces compared to a hollow cone nozzle. Ground and aerial spray losses, quantified as deposition, were numerically lower for the modified irrigation micro-emitter (121.8 ± 43.4 ng cm⁻² and 0.7 ± 0.1 ng cm⁻², respectively) compared to the traditional hollow cone nozzle (447.4 ± 190.9 ng cm⁻² and 3.2 ± 0.4 ng cm⁻², respectively). Overall, the modified irrigation micro-emitter provided similar or superior performance to the traditional hollow cone nozzle with an estimated 12 times reduction in system installation cost.