Clavibacter michiganensis subsp. sepedonicus, Clavibacter michiganensis subsp. michiganensis and Pectobacterium carotovorum subsp. carovorum, are seriously harmful to agricultural production. In this study, the Polygonum orientale essential oils were used as the research object. The formula of botanical bactericide of P. orientale essential oils were determined by solvent screening, emulsifier screening, and toxicity test. Based on the formula, the botanical bactericide was prepared and was carried out to perform in vivo experiments. The preventive effect and therapeutic effect were further analyzed. The experimental results show that ethanol is used as solvent and Tween-20 is used as emulsifier, based on the screenings of five solvents and seven emulsifiers. The formula of botanical bactericide of P. orientale essential oils is obtained as follows (according to the mass ratio): 2% P. orientale essential oils, 8% ethanol, 8% Tween-20, and water (adding up to 100%). The dispersibility, stability, pH value, heat storage stability and cold storage stability of botanical bactericide of P. orientale essential oils prepared by this formula are all up to the standards. In vivo experiments, the preventive effect of the botanical bactericide on Clavibacter michiganensis subsp. sepedonicus range from 30.00% to 88.33%, and the therapeutic effect range from 43.33% to 88.33%; The preventive effect on Clavibacter michiganensis subsp. michiganensis range from 50.00% to 97.00%, and the therapeutic effect range from 26.67% to 96.67%; The preventive effect on Pectobacterium carotovorum subsp. carovorum range from 48.33% to 98.33%, and the therapeutic effect range from 48.33% to 97.00%. In practical application (considering the control effect and the cost), it is recommended that the botanical bactericide of P. orientale essential oils is diluted 80 times, and the implementation methods are immersing the potato tubers and spraying the tomatoes and cabbages. In conclusion, the botanical bactericide of P. orientale essential oils has significant effect against the three plant pathogens in antibacterial assay and in vivo assay. Therefore, it can provide a green way for controlling the three bacterial plant diseases.