Abstract: A laboratory trial was conducted to test the efficacy of OxiDate® in controlling the late blight of potato and tomato fungus, Phytophthora infestans. In addition to the control, three OxiDate concentrations (1:150, 1:100, and 1:50 of OxiDate to water) were used in this study. A total of 17 different late blight isolates collected from New Brunswick, Prince Edward Island, Manitoba, and Quebec were subjected to various concentrations of OxiDate in a replicated experiment using 2-way completely randomized design. Growth of all isolates was inhibited when the 1:50 OxiDate concentration was used. At the 1:100 concentration, growth of 94.1% of the late blight isolates used was completely inhibited. At the lowest concentration of 1:150 OxiDate, the growth of 76.5% of the isolates tested was completely inhibited. The results of this study suggest that OxiDate has the potential to be used in preventing the occurrence of late blight in potato tubers if applied on potatoes in the proper manner after harvest and before storage.