Heat stress and resulting sunburn is a major abiotic stress in perineal specialty crops. For example, such stress to the maturing fruits on apple tree canopies can cause several physiological disorders that result in considerable crop losses and reduced marketability of the produce. Thus, there is a critical technological need to effectively monitor the abiotic stress under field conditions for timely actuation of remedial measures. Fruit surface temperature (FST) is one of the stress indicators that can reliably be used to predict apple fruit sunburn susceptibility. This study was therefore focused on development and in-field testing of a mobile FST monitoring tool that can be used for real-time crop stress monitoring. The tool integrates a smartphone connected thermal-Red-Green-Blue (RGB) imaging sensor and a custom developed application (‘AppSense 1.0’) for apple fruit sunburn prediction. This tool is configured to acquire and analyze imagery data onboard the smartphone to estimate FST. The tool also utilizes geolocation-specific weather data to estimate weather-based FST using an energy balance modeling approach. The ‘AppSense 1.0’ application, developed to work in the Android operating system, allows visual display, annotation and real-time sharing of the imagery, weather data and pertinent FST estimates. The developed tool was evaluated in orchard conditions during the 2019 crop production season on the Gala, Fuji, Red delicious and Honeycrisp apple cultivars. Overall, results showed no significant difference (t₁₁₀ = 0.51, p = 0.6) between the mobile FST monitoring tool outputs, and ground truth FST data collected using a thermal probe which had accuracy of ±0.4 °C. Upon further refinements, such tool could aid growers in real-time apple fruit sunburn susceptibility prediction and assist in more effective actuation of apple fruit sunburn preventative measures. This tool also has the potential to be customized for in-field monitoring of the heat stressors in some of the sun-exposed perennial and annual specialty crops at produce maturation.

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.