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. More