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 <TEX>$Ralstonia$</TEX> <TEX>$solanacearum$</TEX>. All six chemical pesticides applied to the bacterial suspension showed <TEX>$in$</TEX> <TEX>$vitro$</TEX> bactericidal activities against <TEX>$R.$</TEX> <TEX>$solanacearum$</TEX>. Minimal inhibitory concentrations (MICs) of copper hydroxide (CH), copper hydroxide-oxadixyl mixture (CH+O), and copper oxychloride-dithianon mixture (CO+D) were all 200 <TEX>μg/ml</TEX>; MIC of copper oxychloride-kasugamycin (CO+K) mixture was 100 <TEX>μg/ml</TEX>; MICs of both streptomycin- validamycin (S+V) and oxine copper-polyoxine B mixture (OC+PB) were 10 <TEX>μg/ml</TEX>. 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 (<TEX>10⁶</TEX> and <TEX>10⁷</TEX> 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 <TEX>$in$</TEX> <TEX>$vitro$</TEX> against <TEX>$R.$</TEX> <TEX>$solanacearum$</TEX> 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 (<TEX>10⁶</TEX> cfu/ml). Treatment with cinnamon oil and clove oil also suppressed bacterial disease by a higher inoculum concentration (<TEX>10⁷</TEX> 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.