The overall objective of this research program is to develop an effective and sustainable phage-based biocontrol system for citrus canker caused by Xanthomonas axonopodis pv. citri (Xac). Our approach is to develop a pool of virulent (lytic) phages and antibacterial particles called ‘tailocins’ that can be implemented in the field as an alternative to copper for control of citrus canker. In greenhouse trials we have demonstrated that both phage and tailocin cocktails are effective in reducing disease symptoms with one treatment. Tailocins are protein assemblages that function like the tails of phages, by adsorbing to the bacterial cell and then puncturing the cell envelope. Unlike phages, tailocins do not have a capsid and thus inject no DNA, instead relying on the membrane puncturing activity to kill the cell. Like phages, tailocins use tail fibers to recognize specific receptors on the target cell surface. Tailocins are thus potent and specific lethal nanoparticles. Our current efforts have focused on further characterization of both Xac phages and tailocins. Phage CCP504 (Podophage) propagated on homologous host (Xac Block22) had an observed adsorption rate constants of 1.7 X ^-10 ml cell^-1 min^-1, whereas CCP513 (Siphophage) propagated on the same host had an observed adsorption rate constants of 8 X ^-11 ml cell^-1 min^-1. Ongoing studies will determine burst size for each of the phages. Two non-type IV pilus dependent phages that form plaques on Xac are currently being characterized. Since the phages and tailocins will be exposed to natural sunlight when deployed as control agents we have initiated studies to assess the effect of UVC, UVB and UVA light on activity. Initial studies indicate that phage CPP504 and phage CCP513 are extremely sensitive to UVC, less sensitive to UVB and even less to UVA, as indicated by log reduction(s) in activity. Tailocins XT-1 and XT-4 lost less than 10 fold activity when exposed to UVB at energy levels that causes 100-1,000 fold reduction in phage activity. Our previous results indicate that tailocins can be effective in reducing disease as a foliar spray and the observed insensitivity to UVB warrants continued studies and the search for diverse tailocins with activity against Xac.