Xanthomonas arboricola

Xanthomonas arboricola is a bacterium that causes bacterial blight in tree crops, including walnut, hazelnut and stone fruits in the genus Prunus, producing dark, greasy lesions on leaves and fruit from which bacterial ooze can spread further inoculum by rain splash. It is the most devastating blight of walnut and can cause complete yield loss where it is not managed, with epidemics recorded across North America, Europe, the Middle East and Australia, where losses in high-prevalence years have reached an estimated 3.1 million Australian dollars. The bacterium survives dormant in woody tissue over winter, which makes it difficult to manage from one season to the next.