Development of an automated needle-based trunk injection system for HLB-affected citrus trees

Abstract

Trunk injection of chemical compounds is a target-specific method of applying therapeutics that increases applied compound efficiency without compromising environmental safety and has proven to be an effective method to control citrus Huanglongbing (HLB). However, conventional (manual) trunk injection methods are labour-intensive and time-consuming, resulting in high application costs and posing implementation challenges for commercial citrus growers. For this reason, an automated, drill-free system for injecting therapeutic materials into citrus trees to control HLB has been developed. The injection mechanism consists of an end effector and a retractable telescoping positioning arm mountable to a farm vehicle. The system employs a metering pump with adjustable maximum pressure and flow rate for injecting therapeutic materials into tree trunks. This novel technology was evaluated in commercial citrus orchards; the applied volume, injection rate, and injection pressure were measured, and differences based on the time of injection, trunk diameter at the injection point, and irrigation status were examined. The injection was performed until the flow stopped; the injection duration ranged from 30 s to 72 s for all trees. The minimum and maximum volume injected was 53.9 mL and 243.6 mL, respectively, at 44 s and 68 s. The average injection rate per tree ranged from 1.23 mL s−1 to 3.58 mL s−1, and cut-off pressure ranged from 0.97 MPa to 2.01 MPa.