Chemical Pesticides and Plant Essential Oils for Disease Control of Tomato Bacterial Wilt

Efficacy of different control methods was evaluated for disease management of tomato bacterial wilt caused by Ralstonia solanacearum. All six chemical pesticides applied to the bacterial suspension showed in vitro bactericidal activities against R. solanacearum. Minimal inhibitory concentrations (MICs) of copper hydroxide (CH), copper hydroxide-oxadixyl mixture (CH+O), and copper oxychloride-dithianon mixture (CO+D) were all 200 mu g/ml; MIC of copper oxychloride-kasugamycin (CO+K) mixture was 100 mu g/ml; MICs of both streptomycin-validamycin (S+V) and oxine copper-polyoxine B mixture (OC+PB) were 10 mu g/ml. Among these chemical pesticides, treatment of the detached tomato leaves with the 5 pesticides (1 mg/ml), except for OC+PB delayed early wilting symptom development caused by the bacterial inoculation (10(6) and 10(7) cfu/ml). Four pesticides, CH, CH+O, CO+K and S+V, showed disease protection in pot analyses. Six plant essential oils, such as cinnamon oil, citral, clove oil, eugenol, geraniol and limonene, differentially showed their antibacterial activities in vitro against R. solanacearum demonstrated by paper disc assay. Among those, cinnamon oil and clove oil exert the most effective activity for protection from the wilt disease caused by the bacterial infection (10(6) cfu/ml). Treatment with cinnamon oil and clove oil also suppressed bacterial disease by a higher inoculum concentration (10(7) cfu/ml). Clove oil could be used for prevention of bacterial wilt disease of tomato plants without any phytotoxicity. Thus, we suggest that copper compounds, antibiotics and essential oils have potency as a controlling agent of tomato bacterial wilt.