The agronomic practices such as nitrogen fertilizer and population density affect the plant vegetation pattern and cnopy structure and change the pathogenic activities through the microclimate variability generated as a result of these practices and thus modify the disease development. A study was carried out in the field to investigate the effect of three nitrogen rates (0, 150 and 300 kg ha-1) and three tiller densities (600, 120 and 30 tillers m-2) on the development of Septoria tritici on wheat variety Pastiche. The results revealed that nitrogen application increased the severity of S. tritici up to 150 kg ha-1 but doubling this rate produced a slight reduction in the disease level on all leaves assessed both at growth stage (GS) 55 and GS 70 however, the difference was not significant. Increasing shoot density increased the development of S. tritici at GS 55which is attributed to a more favourable microclimate produced with in the leaf canopy at a higher tiller densities compared with produced at the lower tiller densities. However, a very small reduction was recorded at GS 70 at the highest density level when tiller density increased from 120 to 600 tiller m-2. The grain yield progressively increased with the increase of both density and nitrogen levels.