Phytophthora spp attack the roots and trunks of apple trees and are responsible for crown, collar and root rots of apple trees.
- Phytophthora cactorum is the main species responsible for crown and collar rot.
- Occasionally P. syringae may also cause bark rots but this species is more important as a cause of fruit rot in store.
Crown rot and collar rot are distinct diseases:
- Collar rot is a disease of the scion portion of the tree, affecting bark tissues of the lower trunk at or above the soil line. In the UK collar rot is sporadic and a disease of mature trees
- Crown rot is a disease of the rootstock portion of the tree affecting bark tissues of the root crown region. Crown rot is usually important on young trees in orchard establishment.
- Root rot is a disease of the root system and is usually in association with crown rot but can occur in the absence of crown rot. Root rot is usually important on young trees in orchard establishment.