Symptoms
Holly hedges show 'arches' of defoliation that are wider
at the bottom than the top; individual trees lose their leaves
from the bottom upwards. Close inspection reveals circular
black spots on leaves, which soon drop off. Black lesions
can girdle young stems and kill them.
Causes
This disease is caused by a species of the fungus Phytophthora which was first observed in the UK in 1989. Unlike many other Phytophthora species, the holly blight fungus (Phytophthora ilicis) is host-specific and affects only hollies. The fungus is spread within a tree or hedge by rain splash. It is carried further a field by floodwater and surface drainage water, and also on infected plant material. The blight does not appear to kill large branches or whole trees and there are signs that infected trees may recover.
Control
No chemical is available for use in the garden. The only means of control is by seeking to ensure that neither infected plants nor contaminated soil are brought into the garden. Fallen leaves can harbour the disease so collect them up and burn or bin them.