Updated 2026: Stemphylium leaf blight (SLB), caused by Stemphylium vesicarium, is a destructive foliar disease affecting onion crops globally. It also infects other Allium species like garlic, leek, and shallots, and a wide range of alternative hosts including asparagus, tomato, radish, sunflower, and various weeds.

This scan provides a comprehensive overview of SLB, beginning with its identification through characteristic symptoms such as watery, then tan-coloured to dark brown lesions and rapid leaf senescence. The disease’s epidemiology is explored, highlighting its lifecycle, modes of spread, and environmental conditions that favour outbreaks in temperate and subtropical climates.