Summary Peach scab, caused by the fungus Venturia carpophila, is a major threat to peach production world‐wide. Despite its economic impact, the molecular mechanisms driving V. carpophila pathogenicity are poorly understood. In this study, we functionally characterized VcAIP1, a novel effector protein secreted by V. carpophila, and elucidated its roles in promoting infection. More specifically, we showed that the heterologous expression of VcAIP1 in peach leaves significantly increases susceptibility to V. carpophila and other pathogenic fungi, namely Colletotrichum fructicola , Lasiodiplodia theobromae , Monilinia fructicola , and Botrytis cinerea . We also showed that VcAIP1 binds to the peach enzyme PpADC, a rate‐limiting component in polyamine biosynthesis, and suppresses its activity. This interaction reduced peach hydrogen peroxide accumulation, thereby enhancing fungal virulence. Finally, we showed that overexpression of PpADC enhances peach resistance to V. carpophila and the other tested pathogens, while silencing of this gene increases susceptibility. Importantly, exogenous application of polyamines, metabolites synthesized via PpADC, substantially improved peach resistance to multiple pathogens, offering a sustainable strategy for disease management. Collectively, our findings revealed VcAIP1 as a fungal virulence factor that subverts peach defenses by disrupting polyamine biosynthesis and highlight polyamine‐based interventions as promising tools for eco‐friendly peach disease control.