Powdery mildew caused by Blumeria graminis is one of the most widespread diseases in the ‎world, especially in countries with humid and temperate climates. It is a major constraint for ‎barley cultivation. In a strip block design, a greenhouse experiment was conducted in different ‎contrasting environments during the growing seasons of 2019-2020 and 2020-2021. The study ‎investigated the effect of nitrogen fertilization to manage powdery mildew in four Moroccan barley cultivars with different resistance levels: Taffa, ‎Oussama, Rabat 071, and Amalou. Disease severity was assessed weekly as a percentage of the covered leaf area compared to the healthy one to calculate the ‎area under the disease progress curve (AUDPC). Additionally, two agronomic parameters; grain yield and ‎total dry weight were also obtained. Analysis of variance revealed significant environment, ‎genotype, treatment, and their interaction effects on the AUDPC of powdery mildew. The data showed that the application of nitrogen fertilization; N 21%, N33%, and N46%, led to a significant ‎increase in susceptibility to disease compared to non-fertilization. Environments 1 and 2 ‎were more significantly involved in disease severity than environments 3 and 4, and AUDPCs were increased when humid ‎conditions were associated with N21% and N33% supply. This held true for two cultivars, Oussama ‎and Rabat 071, which differed in their susceptibility to the disease. However, the Amalou variety ‎was moderately affected compared to Taffa, which is resistant to powdery mildew disease. ‎Additionally, applying nitrogen supply increases yield under favorable pathogen growth conditions ‎but decreases it under unfavorable conditions. Despite contrasting environmental conditions, these ‎results demonstrate that the effect of nitrogen fertilization on disease management depends on ‎the level of pathogen attacks, the forms of nitrogen fertilizers used, and the growing conditions of ‎both the plant and the pathogen. ‎