Advances in Precision Pesticide Spraying Technology and Equipment

1. Introduction

Against the backdrop of increasing global food demand, chemical pesticides remain a key means of controlling biotic stress in modern agricultural plant protection systems [1,2]. However, traditional application methods have led to severe pesticide waste and environmental pollution, which have become major bottlenecks restricting the green development of agriculture [3,4].

Precision pesticide spraying aims to maximize pest control efficacy while using a minimal pesticide dosage, thereby achieving both pesticide reduction and environmental protection. Emerging technologies—such as variable-rate spraying [5], contour-adaptive spraying [6], controlled atomization techniques [7,8], and novel anti-drift adjuvants [9,10]—are transforming conventional application methods. These innovations are revolutionizing agricultural practices by enhancing the spraying efficiency, minimizing off-target losses, and optimizing the deposition efficacy of pesticide formulations.

This Special Issue, entitled “Advances in Precision Pesticide Spraying Technology and Equipment,” focuses on new technologies and methods that promote the efficient use of pesticides. It features thirteen original research articles, systematically covering nozzle atomization mechanisms, droplet deposition behavior, spray process sensing, novel equipment design and testing, and a comprehensive review of intelligent variable-rate spraying. These studies integrate fluid mechanics, sensing technology, and intelligent control, offering both profound mechanistic insights and practical field-applicable strategies.

2. Source Control: In-Depth Understanding of Spray Atomization Characteristics and Coupling with Chemical Properties

The droplet size, velocity, and spatial distribution of the atomized spray solution directly determine the transport and deposition characteristics of droplets in space. Air-induction sprays have attracted considerable attention due to their drift-reduction potential [11]; however, the internal gas–liquid two-phase flow and liquid sheet breakup mechanism have not yet been fully elucidated.

Yan et al. contributed three representative papers to this Special Issue, systematically analyzing the atomization characteristics of air-induction sprays. First, high-speed camera imaging was used to visualize and quantitatively measure the liquid sheet structure of sprays from air-induction nozzles. Bubbles were identified as a typical feature of the liquid sheets in air-induction sprays, and their disintegration can lead to perforations or interfacial disturbances in the liquid sheet. Compared with standard flat-fan sprays, the spray angle and breakup length of the liquid sheet produced by air-induction sprays were reduced by 23.48% and 16.32%, respectively.

Pesticide formulations vary greatly in physicochemical properties, which can significantly alter liquid sheet behavior and atomization outcomes. Furthermore, the team employed oil-based emulsions, suspensions, and aqueous solutions as spray liquids to investigate the atomization characteristics of air-induction nozzles. It was found that the oil phase in oil-based emulsions exhibits defoaming properties, reducing the number of large bubbles while promoting the formation of holes in the liquid sheet, leading to premature breakup and a shorter breakup length. In contrast, aqueous solutions increased the bubble count and enlarged the liquid sheet expansion angle. When focusing further on the atomization characteristics of oil-based emulsions, they were found to generate smaller, more uniform, and higher-velocity droplets. This finding challenges the simplified perception that air-induction nozzles inevitably produce coarse droplets, revealing a profound coupling between the pesticide formulations and nozzle structures. These works indicate that nozzle selection and operational parameter optimization cannot be decoupled from actual spray solution formulations, and that the balance between drift reduction and effective coverage requires synergistic consideration at the physicochemical property level.

3. Accurate Characterization of Spray Deposition: Modeling of Droplet Deposition Behavior and Deposition Distribution

Whether droplets can effectively deposit on target surfaces after leaving the nozzle directly determines the pesticide utilization efficiency and pest control efficacy [12]. Song et al. established a droplet deposition prediction model for air-assisted spraying scenarios based on the response surface methodology. This model systematically quantified the interactive effects of spray distance, fan wind speed, and deposition height on droplet spatial distribution. The model can be applied to variable-rate spray control systems, providing a quantitative basis for dynamic droplet regulation based on canopy characteristics.

At the microscale, Yan et al. analyzed the deposition behavior of bubble-containing droplets generated by air-induction sprays. Using high-speed microphotography, they observed the impact process of bubble-containing droplets on hydrophilic and hydrophobic surfaces. An interesting finding was that the deposition of bubble-containing droplets can generate a central jet resembling a Worthington jet, and different pesticide formulations significantly altered the maximum spreading diameter of the bubble-containing droplets. On hydrophobic leaves, suspensions and aqueous solutions exhibited droplet rebound, whereas the oil-based emulsion transitioned from rebound to adhesion with increasing concentration. The discovery of this “rebound-to-adhesion transition” is of great significance for improving the pesticide deposition efficiency on difficult-to-wet targets (e.g., hydrophobic leaves). The study also fitted a functional relationship between the dimensionless Weber number (We) and the maximum spreading factor, providing a simple and effective mathematical tool for predicting the deposition behavior of bubble-containing droplets.

4. Breakthroughs in Sensing and Detection Technology: From Spray Flow Rate and Airflow Sensing to Autonomous Navigation of Sprayers

To achieve precision spraying, it is first necessary to “see” and “measure accurately” the spray process and target characteristics. Zhong et al. proposed an in-flight droplet flow rate online monitoring method based on laser imaging. This method requires no physical contact or tracers. By optimizing the imaging angle and extracting the image pixel area and cumulative intensity, a strong linear relationship model with a droplet flow rate was established. Compared with traditional deposition-based indirect measurements, this method achieves true in situ, non-contact, rapid quantification, providing a low-cost, structurally simple solution for real-time spray system evaluation and field monitoring.

Another innovative study was conducted by Liu et al., who used strain-gauge sensors to monitor the aerodynamic characteristics of fruit tree leaves in real time. The team attached flexible strain gauges to the midribs of peach, pear, and apple tree leaves. Combined with high-speed video recording and machine learning algorithms, they successfully extracted leaf responses to airflow, achieving a recognition accuracy as high as 98% for pear leaves. This method overcomes the traditional problem of “airflow without sensing” in air-assisted spraying, making the dynamic response of fruit tree leaves to airflow quantifiable and traceable, and providing a novel sensing approach for optimizing auxiliary airflow parameters and reconstructing within-canopy wind field distributions.

Furthermore, to address the path recognition challenge in orchard automatic navigation, Wei et al. proposed a fruit-tree dripline path detection method integrating 2D LiDAR, RTK-GNSS, and an electronic compass. Through time synchronization, coordinate system construction, point cloud rotation normalization, and the α-shape concave hull algorithm, they achieved precise extraction of the dripline path. This technology provides a reliable spatial reference for autonomous navigation and variable-rate spray path planning in smart orchard operations.

5. Development of Novel Spraying Equipment: From Variable-Rate Sprays to Aerial Spraying Drift Control

Building on breakthroughs in fundamental mechanisms and sensing technologies, the creation of novel spraying equipment is key for translating technologies into practice. Fruit tree canopies are dense and three-dimensional targets, making air-assisted spraying an important method for efficient application [13,14]. During pesticide spraying, precise regulation of the fan airflow rate and spray flow rate based on the canopy demand is critical [15,16]. Zhang et al. developed a LiDAR-based variable-rate orchard sprayer that uses a canopy volume calculation model and an adaptive delayed spray mechanism to achieve real-time dynamic matching of the pesticide output with the canopy volume and travel speed. The system performed excellently: the total error in canopy volume estimation was only 2.84%, and the average error in spray rate control was 8.78%. Deposition tests confirmed uniform coverage within the canopy and minimal drift, providing a practical solution for precision orchard management. Feng et al. systematically investigated the influence of a variable air inlet area on the airflow field distribution of a self-developed multi-outlet air-assisted sprayer. They found that the airflow field consistently exhibited a stable alternating structure of “primary jet–interaction zone.” Changing the air inlet area did not alter the fundamental structure but significantly affected the jet intensity and directional stability. A regression model for the average airflow velocity was established, providing a basis for airflow matching and parameter optimization for different canopy structures.

Addressing the challenge of pesticide application in greenhouse tomatoes, He et al. developed a swing-arm sprayer and systematically evaluated its spraying performance. Through static and dynamic simulations, contact angle measurements, and field trials, they found that adding adjuvants reduced the contact angle on tomato leaves from 49.39° to 40.98° and decreased the relative span (RS) of droplet distribution from 1.305 to 1.021. Field trials showed that the spray coverage was relatively uniform on both adaxial and abaxial sides, demonstrating that the swing-arm sprayer meets the quality requirements for disease and pest control in greenhouse tomatoes.

Fang et al. extended the perspective to the field of forestry aerial spraying. To address the problem of pesticide drift from manned helicopters in forested regions, they proposed a zone-based application strategy that divides the forest into a safe area and edge area, based on the AGDISP aerial spray drift prediction model combined with an optimization algorithm. By adjusting the flight height and speed, they achieved synergistic optimization: moderate and uniform deposition within the forest area and low deposition at 50 m downwind outside the forest area. This research provides an important technical reference for precision forestry spraying.

6. System Integration and Intelligent Variable-Rate Spraying: The Future Path of Precision Spraying

As a review paper in this Special Issue, Jiao et al. systematically summarized the research progress of intelligent variable-rate spraying technology in precision agriculture. The article points out that traditional continuous application methods struggle to cope with the spatiotemporal variability of pests and diseases, leading to excessive chemical input and low efficiency. Three basic architectures currently exist for variable-rate spraying: pressure regulation, flow rate regulation, and pesticide concentration regulation. Pressure regulation relies on the pressure–flow rate relationship but suffers from a narrow flow rate adjustment range and insufficient atomization stability. Flow rate regulation achieves precise control by dynamically adjusting the nozzle orifice area or pulse-width modulation duty cycle, but faces challenges such as mechanical wear and nonlinear relationships. Pesticide concentration regulation, centered on real-time mixing, avoids chemical residue but is highly dependent on fluid properties and mixing efficiency. The article proposes improvement pathways from the perspectives of hardware optimization, control strategy integration, and material innovation, providing a valuable reference framework for future research on variable-rate spraying technology.

7. Conclusions: Towards a New Generation of Spraying Technology Driven by Mechanisms, Empowered by Sensing, and Enabled by Intelligent Decision-Making

The thirteen papers in this Special Issue—ranging from atomization liquid sheet dynamics to deposition distribution in macroscopic canopies; from strain-gauge sensing of aerodynamic characteristics of crop leaves to LiDAR quantification of the canopy volume; and from the anti-drift mechanism of air-induction nozzles to multi-sensor fusion for path navigation—together outline a clear evolutionary trajectory: precision pesticide spraying technology is moving from being experience-oriented to technology-driven, from open-loop control to closed-loop sensing, and from single-component optimization to intelligent system integration.

Future plant protection spraying will no longer rely solely on farmer experience or fixed operational parameters. Instead, based on a quantitative understanding of the entire atomization–deposition–target response process and integrating multi-source information including LiDAR, vision, strain sensing, and BeiDou positioning, it will achieve refined operations of “spray where needed, as much as needed” through intelligent decision-making and precision spray control. We believe that with the further advancement of the fundamental breakthroughs and key technological developments that are showcased in this Special Issue, precision spraying technology will play an increasingly important role in the grand narrative of pesticide reduction, environmental protection, and sustainable agricultural development.