Nitrogen plays a crucial role in plant growth and defence mechanisms, yet its role in plant–pathogen interactions is complex and remains largely unexplored, especially in perennial crops. This study aimed to investigate the effects of controlled nitrogen nutrition levels on disease incidence, fungal communities, and plant physiology and metabolism. Esca is a widespread grapevine vascular disease affecting physiology, xylem integrity, and metabolism. Naturally infected Vitis vinifera L. cv. Sauvignon blanc were subjected to three ammonium nitrate treatments across three seasons, resulting in reduced esca incidence under nitrogen deficiency compared with medium nutrition levels, while excess nitrogen had no significant impact. Nitrogen treatments significantly impacted vine physiology and leaf metabolites, but did not affect fungal wood communities. Nitrogen deficiency significantly reduced stem diameter, photosynthesis, and leaf area, probably decreasing whole-plant transpiration, while excess nitrogen increased these factors, suggesting a key role for plant transpiration in esca incidence. Additionally, nitrogen deficiency led to significantly higher production of phenylpropanoids, particularly flavonoids, in leaf metabolomes compared with the medium level. These findings highlight the pivotal role of nitrogen in the development of esca through alterations in vine morphology, physiology, and metabolism. Fertilization practices may be crucial in the management of plant diseases.Read less <