Antibacterial agent 243 is a potent antimicrobial compound with EC50 values of 0.64 mg/L for Valsa mali, 26 mg/L for allicin, and 0.33 mg/L for tebuconazole. It induces hyphal contraction and collapse, triggers the accumulation of reactive oxygen species within cells, modulates antioxidant enzyme activity, initiates lipid peroxidation, and ultimately causes irreversible oxidative damage to Valsa mali cells.