Potato late blight (PLB), caused by oomycete Phytopthora infestans (Mont) De Bary, is arguably the most important disease of potato in terms of economic losses and environmental and economic impact of the disease management. The Irish Rules model was proposed in the 1950s and is operationally used by the national meteorological agency, Met Éireann, to aid identifying periods of blight conducive weather. Changes in the pathogen population and potato production systems prompted the need to evaluate the model criteria and decision thresholds. The evaluation and subsequent re-calibration of the model using historical disease and weather data led to a significant improvement in diagnostic performance. The modified Irish Rules (MIR) in combination with varietal resistance was further evaluated under field conditions to showcase and empower the use of integrated pest management tools to reliably inform the standard potato late blight management practice under growing conditions and contemporary Phytophthora infestans population in the Republic of Ireland. An extensive evaluation has shown that the MIR model represents an optimum modelling compromise due to the uncertainty of the model input variables, which currently demand simpler modelling approaches, such as the MIR. However, constant technological advancements will lead to improvements such as, in numerical weather prediction, and will provide possibilities for more complex risk prediction modelling. Hence, a new model which provides a more realistic interpretation of the P. infestans lifecycle is proposed. To facilitate a shorter time-gap between PLB model evaluations, the entire analysis is implemented in a single open source programming environment, completely reproducible and hosted on an open access server. Finally, the recommendations for a modification of the current model, its operational use are proposed, as well as suggestions for further research and improvement of the practical application of decision support in potato late blight forecasting.