The first research by Leonardo Da Vinci described in detail the workings of tree anatomy and physiology resulting in the "Rule of Trees"
Here is some more academic articles should you want more detail:
Refining trunk injection strategies for controlling folicutar insect pest and disease in Michigan State University. Charles Clark Coslor. A dissertation Entomology—Doctor of Philosophy 2017https://bsapubs.onlinelibrary.wiley.com/doi/abs/10.1002/j.1537-2197.1920.tb05558.x
Grape vine injection of salicylic acid . Salicylic acid treatment of grape berries retards ripening. E Kraeva, C. Andary, A. Carbonneu and A. Deloirehttps://patents.google.com/patent/WO2011007104A2/en
Spiers A. Ward BG, 2001 - Injection treatment for control of plant diseases. In Patent Cooperation Treaty, Vol PCT WO 01 / 76355A1
Frank L. Howard, Kingston, Nestor E. Caroselli, COMPOSITIONS FOR TREE THERAPY
J. Hu, J. Jiang, and N. Wang Control of Citrus Huanglongbing via Trunk Injection of Plant Defense Activators and Antibiotics Phytopathology 2018 108:186-195http://dx.doi.org/10.1094/PHYTO-05-17-0175-R
Efficacy of systemic acquired resistance inducers in olive leaf spot management Australasian Plant Pathology 42(2)
Paap, T., de Beer, Z.W., Migliorini, D., Nel, W.J., Wingfield, M.J., 2018. The polyphagous shot hole borer (PSHB) and its fungal symbiont Fusarium euwallaceae: a new invasion in South Africa. Australasian Plant Pathology 47, 231-237.