Incidence of Late Blight (Phytophthora infestans) on Irish Potato in Jos Plateau, North Central Nigeria

Irish potato (Solanum tuberosum) cultivation on the Jos Plateau of Plateau State is critically dependent on climatic conditions that, while favourable for the crop, also support the development of Phytophthora infestans, the causal organism of late blight. Late blight remains one of the most economically significant plant diseases in highland African potato production systems. This study evaluated the incidence and severity of late blight across potato farms in Barkin Ladi, Bokkos, and Mangu local government areas of Plateau State during the 2023 growing season. Sixty farms were included in the survey, with disease assessment carried out weekly from early-season establishment to harvest. Disease severity scores were converted to area under disease progress curve values for comparative analysis. Late blight incidence reached 88 percent across surveyed farms by mid-season, with average severity scores exceeding the economic threshold used to justify protective fungicide applications. Resistance to commonly used metalaxyl-based fungicides was suspected based on field observations of disease progression despite routine chemical applications. Farmers reported increased fungicide costs contributing to reduced profitability, with some opting to harvest early to minimise losses. The study highlights the urgent need for the deployment of late blight-resistant potato varieties and a systematic evaluation of effective fungicide rotation programmes suitable for Jos Plateau conditions. Keywords: Irish potato, late blight, Phytophthora infestans, Plateau State, disease severity.