Stereo vision controlled variable rate sprayer equipped with an automatic electric variable air assist system

Authors: Jeon, Hongyoung; Zhu, Heping

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2026
Publication Date: 5/31/2026
Citation: Jeon, H., Zhu, H. 2026. Stereo vision controlled variable rate sprayer equipped with an automatic electric variable air assist system. Computers and Electronics in Agriculture. 250. Article 111979. https://doi.org/10.1016/j.compag.2026.111979.
DOI: https://doi.org/10.1016/j.compag.2026.111979

Interpretive Summary: An orchard sprayer with an air assist system is commonly used to apply crop protection products (CPP) to specialty crops for pest protection and ensuring crop quality and yield. An air assist system for an orchard sprayer has critical functions in CPP applications, carrying CPP sprays to crop canopies and assisting penetration into the canopies. However, common air assist systems for the sprayers are often oversized when used in other crops. As a result, they often provide excessive air assist for CPP sprays, and generate unintended spray drift. An electric variable air assist system (EVAAS) was developed to address such issues by controlling airflow for based on canopy presence, size and density. EVAAS was integrated into a stereo vision controlled variable rate sprayer to adjust spray outputs and airflows simultaneously based on canopy characteristics. The sprayer with EVAAS was tested for its spray canopy depositions and spray drift in an apple orchard compared to a conventional sprayer and a variable rate sprayer. The results showed the sprayer with EVAAS increased average spray canopy depositions by approximately 54.7% and reduced spray drift by approximately 77.4% while reducing the spray volume approximately 41.3% compared to a conventional sprayer. The outcomes of this work can be used to develop automatic specialty crop sprayers that adjust its sprays and airflows based on size, presence, and densities of crop canopies to reduce spray drift.

Technical Abstract: Protecting fruit and ornamental trees from pest attacks with plant protection product (PPP) is an imperative task to preserve their quality and quantity. However, consumer concerns regarding unintended environmental contaminations from PPP applications are reasonable as PPP spray applications for trees are commonly assisted by vigorous airflow which often carries sprays beyond tree canopies. Adjusting airflow intensities in real time is a challenging task as mechanical actions to accelerate and decelerate a typical axial fan for air assist spray are slow. To overcome such challenge, an electric variable air assist system (EVAAS) was developed with electric fans, custom designed air duct, a microcontroller, and a battery. The system was integrated to a stereo vision guided sprayer to provide air assist at its exit speed from 4.1 to 9.8 m s-1 based on presence of tree canopies. A field experiment for evaluating the performance of the stereo vision guided sprayer with the EVAAS against conventional and variable rate sprayers with conventional air assist system was carried out. The data from the experiment showed the sprayer with the EVAAS applied approximately 41.3% less spray volume and 65% less air volume than the conventional constant-rate sprayer. Also, the new sprayer increased average spray depositions on trees by 29.9%–105.8% and significantly increased (p<0.05) overall average spray deposition by 54.7%. Moreover, the sprayer with the EVAAS significantly reduced (p<0.05) overall average spray drift (a reduction of approximately 77.4%) compared to the conventional sprayer with conventional air assist system while the variable rate sprayer with conventional air assist system significantly reduced (p<0.05) overall average spray drift by approximately 49.4%. Although the system presented herein was a prototype needing more evaluations, the results of this preliminary study were promising and showed the potential of the EVAAS to substantially increase the application efficiency and reduce spray drift for tree crops.