Efficacy of Fungicide Programmes for Control of Late Blight (Phytophthora infestans) on Potato in Plateau State, North Central Nigeria

Late blight caused by Phytophthora infestans is the primary yield-limiting disease of potato on the Jos Plateau, where epidemic development is closely coupled with rainfall patterns during the growing season. The rapid evolution of fungicide resistance in P. infestans populations has complicated chemical management, necessitating evidence-based fungicide programme evaluation under Nigerian highland conditions. This study evaluated the field efficacy of six fungicide programmes for late blight control in potato crops across two experimental sites in Plateau State over the 2023 and 2024 growing seasons. Programmes included protectant-only, systemic-only, alternation, and mixed curative-protectant schedules applied at seven-day and fourteen-day intervals. Disease severity was assessed weekly, and area under disease progress curve values computed for each treatment. Marketable yield and economic return were analysed for each programme. Seven-day alternation programmes combining cymoxanil with mancozeb and chlorothalonil produced the greatest disease suppression, reducing area under disease progress curve by 81 percent relative to the unsprayed control and yielding 24.2 tonnes of marketable tubers per hectare. Fourteen-day single-product systemic programmes showed evidence of reduced efficacy consistent with declining metalaxyl sensitivity, a finding warranting further resistance monitoring. Results indicate that interval and programme composition are both critical determinants of effective late blight management. The study recommends formal revision of fungicide use guidelines for plateau potato growers and establishment of a disease forecasting alert system linked to rainfall data. Keywords: late blight, Phytophthora infestans, fungicide, potato, Plateau State.