Every county in the Bay Area has at least a few documented cases of sudden oak death, so containment here might seem like a lost cause. However, since Phytophtora ramorum, the pathogen that causes the disease, shows up in discrete patches, gardeners can help prevent its spread even within the 14 coastal counties with known cases.
Exceptional care should be taken in the wildland/urban interface, and it’s best not to plant the principal foliar hosts: rhododendron, camellia, viburnum, pieris, and bay laurel. Regionally propagated plants are considered safer, and, if there’s a chance of infection, plant pathologists suggest an eight-week quarantine for new plants, in an area away from vulnerable species.
Although compost seems to be safe, mulch may be infested. Vulnerable landscape trees can be protected with the phosphonate-based fungicide Agrifos, the only currently tested and approved treatment to prevent infection or slow down the progress of the disease in newly infected trees. Agrifos must be applied by a licensed pest-control applicator. But it will not cure an infection, and without a lab culture, diagnosis is uncertain, since many other diseases have similar symptoms.
For more information:
Frederique Lavoipierre wrote a more detailed article geared toward gardeners in the fall 2004 issue of Pacific Horticulture magazine. The article is available for download as a PDF here:
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