## 1 Introduction  
The United States (US) is the third largest producer of the apple (_Malus domestica_) in the world after China and European Union [1]. Total fresh market apple production in the US in the year 2018 was 3.4 million tons with a total worth 3 billion dollars--out of which 73% was produced in Washington State (WA) [2]. Commercial apple production requires numerous applications of agrochemicals including insecticides, fungicides, foliar nutrients, and plant growth regulators with the most common application equipment consisting of air-blast sprayers [3, 4]. However, this technology has a high tendency to produce off-target spray drift, defined as the movement of sprayed droplets through the air away from the intended target [5]. Off target spray drift has been reported as a major contributor of environmental contamination and is among the top ten contributors causing human health risk around the world [3; 6; 7; 8]. Increasing market demand, restricted labor availability, and mechanization advances have led to substantial modification to orchard systems with widespread transition to tall spindle, v-trellis, and bi-axis architectures [9; 10; 11; 12]. Such architectural changes of moving from spherical to compact linear architectures have further intensified spray drift with traditional sprayers with large air volumes [12; 13]. Growers have adopted several modified forms of air-assisted sprayers (e.g., vertical tower sprayer, tunnel sprayers, and electrostatic sprayers) which have demonstrated encouraging results in drift reduction. However, equipment size, maneuvering difficulties, high operational cost, and inconsistent performances based on canopy size are some of the reported difficulties associated with these technologies [3; 14; 15]. Tractor-based sprayers also contribute to soil compaction and crop loss due to physical impact between fruits and equipment [16; 17]. Since heavy air-blast sprayers cannot be operated on saturated soils, critical agrochemical application timings can be missed, leading to crop loss [18]. Thus, there is a need and growing interest in the development of efficient spraying techniques designed specifically for modern orchard architectures. Recently, fixed spray application systems deemed Solid Set Canopy Delivery Systems (SSCDS) have been suggested as an alternative to tractor based sprayers for high density orchards and vineards [12]. SSCDS have been evaluated for use in high-density apple orchards, vineyards, blueberries and other tree fruit systems with most of the work focusing on system development and measurement of deposition and coverage [12; 18; 19; 20; 21; 22; 23]. SSCDS pest management efficacy has been demonstrated for high-density apple orchards in Michigan and New York, USA [24; 25; 26]. A pneumatic spray delivery system was developed by [PERSON] et al. [21] to overcome the issue of non-uniformity in spraying associated with a hydraulic spray delivery approach. Efforts have also been made to automate the operational stages of a SSCDS for large-scale replacements and commercial adaptation. [PERSON] et al. [27] developed an electronic control system and a spray control unit for wireless and remote actuation of the SSCDS variant under study. One of the key design constraints for SSCDS is that they rely on a large number of nozzles/micro-emitters (3000-10,400 per ha) and their placement within the canopy considerably affect the spray deposition and coverage [18; 20; 28]. For example, while a shower down configuration with a single nozzle atop each tree was reported as the simplest and most economical configuration, it provided reduced spray deposition in lower canopy regions and underside of leaves [22]. Another SSCDS configuration with hollow cone nozzles installed in a 3-tier (6 nozzles per tree) provided higher levels and more consistent spray deposition and coverage in a high-density apple orchard [28], but can cost prohibitive at approximately $208,000 ha\({}^{-1}\) (10,400 nozzle-assembly ha\({}^{-1}\) at average $20 nozzle-assembly\({}^{-1}\)).