Collar rot is a disease of the trunk of woody plants and trees and caused by the fungus Phytophthora. It is favoured by wet weather and is soil borne and can survive for many years as spores. The spores germinate to release zoospores which move in soil moisture to infect the roots/root crown or scion through cracks, or damaged trunks. The first symptoms of collar rot may be poor growth, leaf yellowing or premature autumn colours. A water-soaked, weeping area on the trunk which has a distinct orange/red-brown rot under the bark is characteristic of collar rot.