The causative organism is Fomes noxius and spread of infection is by root contact Violet disease is important only in Assam and even that area occurs only in heavy, clay soils which are prone to waterlogging. Visible growth of the causative organism, Sphaerostilbe repens, is seen as thick, purple-black strands under the dark of affected roots. It is not known, however, whether the fungus is responsible for death or develops after the root dies as a consequence of waterlogging.