A yellow-pigmented, Gram-negative, aerobic, salicin utilising bacterium-identified as Xanthomonas campestris pv. populi was isolated from one year old stems of S. matsudana X alba‘Aokautere’ willows exhibiting stem necrosis. Although the bacterium was isolated from necrotic stem tissue almost in pure culture it was not pathogenic to vigorously growing material of S. matsudana X alba‘Aokautere’ in field inoculations. Stress and predisposing climatic conditions during winter (frost, rain, wind, mild temperatures) are thought to have favoured the initial infections of this opportunistic pathogen. This disease is not considered serious.