Alternaria solani is causing early blight and thereby yield reduction in the potato production. The pathogen is today mainly controlled by fungicide applications. The severity of early blight can vary largely among fields. The aim of this study was to gain understanding of what field and management parameters are the most important for early blight severity to create more farm-specific fungicide treatment recommendations. Over three seasons, 2019–2021, 52 field plots were observed at farms in southern Sweden. In each field a 24 m × 24 m plot was left untreated against early blight. However, late blight fungicides were applied. The disease severity was scored twice in the untreated plot and information about various soil/plant parameters and farmer’s management was collected from each field. In addition to the observational study, field trials were performed in 2021 and 2022, evaluating the effect of potassium fertiliser levels on severeness of infection. We found that the soil composition was of significant importance for the severity of infection, in particular the sand, clay, and potassium content. The early blight severity was directly positively correlating with a high sand content. Low levels of leaf potassium increased the severity of early blight infection, and this observation was confirmed in field trials where different levels of potassium fertiliser were applied. Further no reduction in disease severity was observed with a four-year crop rotation. With knowledge about field and management factors that influence disease, field-specific recommendations can be developed supporting an integrated pest management strategy for early blight to reduce and optimise the fungicide usage.