Efficacy of copper and copper alternatives for management of bacterial spot on tomato under transplant and field production.
Bacterial spot of tomatoes (BST) caused by Xanthomonas perforans, is a ubiquitous disease of tomato in field and transplant operations in Florida. For disease management, producers rely heavily on copper or copper-mancozeb sprays, which are often ineffective due to the high prevalence of copper-tolerant Xanthomonas strains. In this study, 19 different chemical agents, biological control agents, plant defense activators, and novel products were evaluated for their ability to manage bacterial spot on tomato seedlings and in the field. Efficacies of single rotations or tank mixes of several compounds were compared to a non-treated control and a copper standard on seedlings. Stand-alone applications of acibenzolar-S-methyl (ASM), copper octanoate, quinoxyfen, oxysilver nitrate, and pentasilver hexaoxoiodate significantly reduced disease compared to inoculated controls. Seedling programs that included either ASM or copper octanoate significantly reduced disease compared to the control. Oxytetracycline and streptomycin were ineffective at reducing disease severity under high disease pressure in seedling trials. Although there were significant differences in disease severity among treatments, there were no significant difference in the overall yield among treatments across field trials. Overall, ASM provided significant disease reduction as a stand-alone or in a program with other compounds in both the greenhouse and field. However, copper octanoate alone or as a tank mixture with other compounds was only effective for seedling production. The use of alternative compounds should improve tomato health, reduce the introduction of disease inoculum into fields, and reduce residual copper in the environment.