Pest of the month: Sudden oak death

Infected Azalea leaves

Infected Azalea leaves

Pest of the month: Sudden oak death (Phytophthora ramorum)

Category name: Fungi

Importance: Emergency disease

Symptoms: In oak trees, the earliest symptoms are the appearance of a bleeding canker, burgundy-red to tar-black thick sap, oozing on the bark surface. The disease is typically found from the root crown (the area where the trunk fans out to the roots) to a height of 2 meters. Symptoms on secondary hosts include leaf spots, leaf blight, stem and twig cankers, and shoot tip and branch die-back. Infections on Rhododendron cause brown lesions on leaves and young stems. On Viburnum, the infection usually occurs at the stem base causing the plants to collapse.

Transmission: The organism can be spread in soil and water. It can survive in moist conditions for at least one month. In USA it has been recovered from soil carried on hikers shoes. The fungi can reproduce rapidly on leaf surfaces, allowing rapid build-up of Phytophthora spores, which serve as a source of infection.

Favoured by: Phytophthora ramorum is a cool temperature organism, with optimum growth at 20° C. Infection of foliar tissue requires cool temperatures and free water.

Infected tree symptoms

Infected tree symptoms

Host range: A disease primarily of oak trees (Quercus spp.). Secondary hosts, which are highly susceptible, include Acer, Azalea, Camellia, Rhododendron, Viburnum, Pieris, Syringa and Kalmia.

Further industry pest information is available at

Pest Fact Sheet – Phytophthora ramorum: a biosecurity threat to the Australian nursery industry available here

An initiative of the National Nursery Industry Biosecurity Program (NY15004) and the ‘Building the resilience and on-farm biosecurity capacity of the Australian production nursery industry’ Project (NY15002).