Forecasting Potato Late Blight ( Phytophthora infestans ) Using Weather‐Based Models in Major Potato‐Growing Regions of Ethiopia

Late blight, caused by Phytophthora infestans , is the most serious threat to sustainable potato production in Ethiopia, causing major yield losses and forcing the farmers to rely heavily on fungicides, which increase production costs and contribute to environmental pollution. Potato growers usually apply fungicides without a reliable potato late blight management decision support system. There is a gap in the development of weather‐based potato late blight forecasting models suitable for Ethiopia's diverse agro‐ecological conditions. This study was carried out during the 2022, 2023 and 2024 main cropping seasons at three major potato‐producing areas: Haramaya, Holeta and Negele Arsi to identify key weather variables significantly influencing potato late blight onset and progression, and develop location‐specific weather‐based forecasting models. The number of rainy days and mean minimum temperature recorded 5 and 7 days before disease assessment dates were highly significant ( p < 0.001). Variables showing strong Pearson correlation with absolute rate of disease severity change ( r = 0.75–0.93) were selected for modelling. General Linear Mixed Models (GLMM) revealed that each additional rainy day increased disease severity by 0.12, 0.14 and 0.07 at Haramaya, Holeta and Negele Arsi, respectively, on the susceptible variety Jalene, and by 0.09, 0.10 and 0.07 on the moderately resistant variety Gudene, assuming constant temperature. Optimal management intervention times were identified as 36–38, 45–47 and 48–50 days after planting (DAP) at Holeta, Haramaya, and Negele Arsi, respectively, ahead of disease onset at 43, 50 and 55 DAP, respectively. Overall, the results show that adopting these area‐specific, weather‐based forecasting models can help farmers improve the timing of late blight management and reduce unnecessary fungicide use.