Biopesticides provide inadequate control of three foliar bacterial diseases of tomato transplants

There are three important diseases caused by bacterial pathogens affecting tomato foliage on seedlings in the greenhouse and on mature plants in the field: bacterial canker, bacterial spot, and bacterial speck. Their causal agents are seedborne and the greenhouse environment is conducive for their multiplication and spread; therefore, control measures should be targeted to transplant production to reduce the risk of epidemics in the field. A tank-mix of copper and mancozeb or streptomycin are standard treatments to prevent or manage these diseases in the greenhouse, but the presence of copper and/or streptomycin resistant strains makes it difficult to achieve consistent control. Increasing demand for biopesticides to avoid control failure due to pesticide resistance and reduce the use of conventional pesticides has led to many products being developed. We evaluated three registered biopesticides (Regalia, Stargus, and TerraGrow) and five products in development: three botanicals (AOMMA-Agro, CranShield Plus, and CranProtect), a biological bacterial biofilm inhibitor (SP8010), and Zinkicide. Products were applied singly or in combination to assess their efficacy against three bacterial diseases of tomato seedlings caused by four pathogens, compared to a tank mixture of copper plus mancozeb alternated with streptomycin (grower standard) and a non-treated control. The grower standard provided the best control in three of the four experiments, while the biopesticides were inconsistent or ineffective in controlling each of the four pathogens in this study.