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Frequently Asked Questions related to Sudden Oak Death
4 September 2002

Prepared by the California Oak Mortality Task Force

What is Sudden Oak Death?
It's a highly contagious disease that can infect and quickly kill several species of native California oaks. It first appeared in 1995 in Marin County and has since killed tens of thousands of oaks and tanoaks along the state's northern coast.

What causes Sudden Oak Death?
It's caused by a fungus-like brown alga called Phytophthora ramorum (phy-TOFF-thoruh ruh-MOR-um), which was identified in 2000 by University of California researchers at the Berkeley and Davis campuses. P. ramorum is related to the organism that caused the Irish potato famine. It may have entered the U.S. on imported nursery plants.

Does this organism affect other trees and plants?
Yes, it also has been found to be causing disease, similar to Sudden Oak Death, in coast redwood and Douglas fir, as well as 14 other plant species in the United States, including madrone, bay laurel, buckeye and rhododendron. In Europe, it also has been found in viburnum.

What are the symptoms of Sudden Oak Death and related diseases?
In oaks, the first symptom is typically a bleeding or oozing of thick, dark reddish-brown sap from the trunk. With tanoaks, the first symptom is dropping of new leaf growth. Beetles then attack the weakened trees, and in the later stages of decline, decaying fungi are seen on the trunks of oaks and tanoaks. An infected oak will form a girdle or ring of dead tissue beneath the bark of its trunk, which blocks the flow of water and nutrients. As a result, the tree may die in just a few weeks. Signs of the disease caused by P. ramorum in redwood have been observed only in the needles and very small branches of redwoods. In redwoods, the infected seedlings became yellowed and discolored. Douglas fir seedlings showed a similar, but more intense, response.

How do scientists know that these diseases are caused by P. ramorum?
First they take DNA samples from trees to see if P. ramorum is present. Then, in the laboratory, they see if they can cause symptoms of the disease by infecting healthy seedlings with that fungus-like organism. Where have Sudden Oak Death and other P. ramorum diseases been found? These diseases have been identified in trees and plants in Alameda, Contra Costa, Humboldt, Marin, Mendocino, Monterey, Napa, San Mateo, Santa Clara, Santa Cruz, Solano and Sonoma counties.

How are Sudden Oak Death and related diseases spread?
P. ramorum, the organism that causes these diseases, is spread via spores and cysts. During wet weather some affected plants, such as bay laurels, release spores that can travel in moist soil and through the air. People and animals can also track spores to uninfected areas. Sometimes spore-containing cysts form and accumulate in the bed of dead leaves beneath the trees and can easily be spread by people and animals walking underneath the trees. These spores and cysts also can be carried in the plant material of dead hosts.

What impact will these diseases have on California's landscape?
It is anticipated that Sudden Oak Death will spread to more areas of California. Since various tree and plant species seem to be more severely affected by P. ramorum than others, it may take years before the full ecological impact of this disease-causing organism will be known.

How can Sudden Oak Death and related diseases be prevented?
Preventing the movement of infected leaves, wood and soil is critical to slowing the spread of P. ramorum to other areas. People who have been in infected areas should clean and disinfect their shoes and vehicle tires with bleach. Chemical treatments for preventing these diseases are being tested. Currently there are no treatments approved for the prevention or cure of Phytophthora ramorum.

How is movement of tree and plant materials regulated?
The California Department of Food and Agriculture, the California Department of Forestry and Fire Protection, and County Agricultural Commissioners, in conjunction with the U.S. Department of Agriculture, are responsible for enforcement of state and federal regulations designed to slow the artificial spread of Phytophthora ramorum.

Where can I get more information online?
Sudden Oak Death Online Media Kit, UC Division of Agriculture and Natural Resources
Marin County UC Cooperative Extension Office
California Oak Mortality Task Force
SOD Mapping Project
California Oaks Foundation

Media contacts:

Matteo Garbelotto, assistant adjunct professor of ecosystem science and Cooperative Extension Specialist, UC Berkeley, (510) 643-4282,

David Rizzo, associate professor of plant pathology, UC Davis, (530) 754-9255,

Katharine Facino, California Oak Mortality Task Force, (916) 651-9182,

Sarah Yang, UC Berkeley Public Affairs, (510) 643-7741,

Patricia Bailey, UC Davis News Service, (530) 752-9843,