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Sudden Oak Death is caused by a funguslike pathogen recently identified by UC scientists and named Phytophthora ramorum. Since its appearance in 1995, Sudden Oak Death (SOD) has killed hundreds of thousands of coast live oak, black oak, tanoak and Shreve oak in northern California. It can also infect leaves and branches of rhododendron, buckeye, madrone, manzanita, bigleaf maple, bay laurel, and evergreen huckleberry. Two species of East Coast oaks, northern red oak and southern red oak, are also susceptible to P. ramorum, according to UC Davis plant pathologist Dave Rizzo.

DISTRIBUTION:  Sudden oak death has been found as far north in the state as Humboldt County and as far south as Big Sur in Monterey County. To date, SOD has been identified in 14 California counties: Alameda, Contra Costa, Humboldt, Lake, Marin, Monterey, Napa, San Francisco, San Mateo, Santa, Clara, Santa Cruz, Sonoma, Mendocino. Solano. In Oregon, Sudden Oak Death has been confirmed in Brookings, a small town in the southwestern corner of the state. 

SYMPTOMS:  Bleeding or oozing of a dark reddish-brown thick sap is the first symptom to appear on true oaks. It typically occurs on the lower portion of tree trunks (less than 10 feet) but has been found as high as 60 feet. On tanoak, the first symptom is drooping of new growth. Beetles attack weakened trees. Wood decaying fungi are seen in the later stages of decline on the trunks of oaks and tanoaks. 

PREVENTION:  Preventing the movement of infected leaves, wood and soil will be critical to slowing the spread of the fungus to other oak woodlands, such as the Sierra Nevada. Plant material and soil should not be moved from coastal areas. Any wood already moved elsewhere should be burned. Visitors to coastal forests should clean their tires, shoes and animals' feet thoroughly before leaving the area. Construction workers should wash equipment well and should not move dirt from one place to another. Ornamental plants, such as rhododendrons, that may be hosts should not be moved from infected counties unless certified to be free of the pathogen.

QUARANTINES:  Oregon, Canada and South Korea have enacted quarantines on oak products from California. 

LOOK-ALIKE DISEASE:  Phytophthora cinnamomi can produce identical symptoms in oak trees. Scientists differentiate this fungus from Sudden Oak Death by using a lab test. P. cinnamomi can infect about 1,000 plant species. It can kill oaks, rhododendrons and other nursery plans and agricultural crops including almond, walnut and avocado trees.