AbstractKiwifruit, a nutritious fruit consumed globally, is affected by kiwifruit bacterial canker (KBC) caused by Pseudomonas syringae pv. actinidiae (Psa), which is a major biotic stress that adversely impacts its cultivation and production. KBC control is still challenging owing to the evolution of resistant populations of Psa, the environmental risks associated with copper bactericides, and lack of effective bactericides. Therefore, to develop novel and efficient bactericides against Psa, a matrine (MT)‐5‐methylsalicylic acid (5‐OMESA) salt (MOS) is synthesized and its antibacterial activity is analyzed. The newly synthesized compound is more antibacterial against Psa than the commercial bactericide thiazole copper (TC). MOS significantly disrupts the membrane structure of Psa and penetrates the cells more efficiently. In addition, it has high affinities to the Psa FtsZ protein and DNA helicase, which probably contribute to its bactericidal activity. Subsequently, the encapsulation of MOS into a supramolecular nanocarrier hydroxypropyl‐β‐cyclodextrin (HPCD) and the fabrication of a nano formulation (MOS@HPCD) result in superior solubility, penetration, foliar deposition and wettability, sustained release, and prolonged protection against Psa. The in vitro and in vivo control efficiencies of MOS@HPCD against Psa are markedly enhanced compared to those of MOS. This study proposes a promising supramolecular material to control KBC.