Angular leaf spot, caused by P. syringae, is one of the most important bacterial disease of watermelon. For disease management, growers rely on copper bactericides, which are effective after the first two weeks of transplanting, while they couldn't be applied before that due to the high phytotoxicity they may cause to the plant. This study was undertaken to evaluate the antibacterial activity of three new copper composites, core-shell copper (CS-Cu), multivalent copper (MV-Cu), and fixed quaternary ammonium copper (FQ-Cu), as potential treatments to control the disease before the emergence of the first true leaf where copper is not available, and to identify the possibility of applying the newly designed copper composites during that period to significantly reduce secondary dispersal of disease inoculum. In vitro, 50 μg/ml of metallic copper from MV-Cu and FQ-Cu significantly reduced the P. syringae populations after 2hrs of exposure compared to the untreated control (P= 0.05) and were more effective than using the Kocide^® 3000. Greenhouse studies demonstrated that MV-Cu and FQ-Cu significantly reduced the disease incidence compared to both Mankozeb+ Kocide^® 3000 and untreated control when using the seed inoculation method. In contrast, none of the nano-composites significantly reduced disease incidence when using the spray inoculation method. MV-Cu and FQ-Cu managed to significantly reduce seedling to seedling disease transmission under greenhouse conditions (P = 0.05). This study highlights that copper composites have the potential to manage P. syringae in the first two weeks of transplanting and reducing the contamination rate from infected to healthy transplants