The development and evolution of trunk injection mechanisms -a review

Trunk injection of chemicals is an alternative to conventional methods of applying plant protection products, and it can potentially deliver the exact dosage of therapeutic material required by the plant without undermining environmental protection and human health. Although trunk injection has proven to be an effective method for managing systemic pathogens, several studies have highlighted limitations for large-scale commercial tree crop applications because of the manual process involved, emphasising the need for an automated injection system. The process of trunk injection involves the steps of hole creation on the main stem of a tree and the injectate delivery of the therapeutic material. Injection mechanisms can be categorised based on the approach of creating an injection port, method of injectate delivery, and pressure source used to apply the injected material. This review article extensively investigates the development of various trunk injection mechanisms, operating principles, and practical applications, critically presenting advances in tree injections and highlighting gaps in knowledge to guide the development of automated injection systems. This review also discusses optimum injection parameters, such as hole size, above-ground injection height, number of injection ports, injection rate, and pressure. Additionally, it covers other factors such as tree variability, leaks and backflow, and the question of air exclusion during injection and wounding that may contribute to the design of an effective injection device. Furthermore, recent advances in developing an automated injection device are highlighted.