Sudden Oak Death

In 1995 the death of large numbers of tanoak trees was observed in Marin, Santa Cruz, and Monterey counties. In 1999 emergency funding for research was provided to investigate the cause of death of oaks and tanoaks in Marin County. In 2000, the cause of this infection was identified to be Phytophthora ramorum, a water mold commonly called Sudden Oak Death. This disease has spread to twelve coastal counties.

Plants infected with P. ramorum have been observed in 12 counties along the west coast of California: Humboldt, Mendocino, Sonoma, Napa, Solano, Marin, Contra Costa, Alameda, San Mateo, Santa Clara, Santa Cruz, and Monterey.

As of spring, 2003, there are 26 plant species known to be susceptible to the disease. These species are infected in one of two ways: in the trunk or in the leaves and twigs. The species infected in their trunks often suffer lethal damage. These include several species of oak trees.

Plants Susceptible to Sudden Oak Death Trunk Infection, Often Killed:
California black oak (Quercus kelloggii) *
Canyon live oak (Quercus chrysolepis) *
Coast live oak (Quercus agrifolia) *
Shreve's oak (Quercus parvula var.shrevei)*
Tanoak (Lithocarpus densiflorus)*

The species infected in their leaves and twigs usually do not die, but some may act as hosts that spread the disease by wind-borne raindrops. These plants may develop leaf spots and blotches.

Plants Susceptible to Sudden Oak Death Leaf/Twig Infection,
Usually Not Killed But May Spread The Disease
Arrow wood (Viburnum)*
Big leaf maple (Acer macrophyllum)*
California bay laurel (Umbellularia californica)*
California buckeye (Aesculus californica)*
California coffeeberry (Rhamnus californica)*
California hazelnut (Corylus cornuta)
California honeysuckle (Lonicera hispidula)*
Camellia (Camellia)
Cascara (Rhamnus purshiana)
Coast redwood (Sequoia sempervirens)*
Douglas-fir (Pseudotsuga menziesii)*
Huckleberry (Vaccinium ovatum)*
Madrone (Arbutus menziesii)*
Manzanita (Arctostaphylos manzanita)*
Pierus (Pierus)
Poison oak (Rhus diversiloba)
Rhododendron (Rhododendron spp)*
Salmonberry (Rubus spectabilis)
Toyon (Heteromeles arbutifolia)*
Victorian box Pittosporum undulatum)
Western starflower (Trientalis latifolia)*

* recognized as a regulated host by the United States Department of Agriculture, Animal and Plant Health Inspection Service - Plant Protection and Quarantine (USDA-APHIS-PPQ), and by the California Department of Food and Agriculture (CDFA).

As of spring, 2003, Sudden Oak Death has not been identified on Stanford University lands.

In Grounds Services, we watch for problems in our oaks at Stanford, and have a monitoring program in place to keep records of select trees to record change in their health. We are also fortunate to have observant citizens report to us additional observations of possible problems with our prized trees. Alert to the potential devastation of Sudden Oak Death, we keep informed of results of recent studies by Bay Area leading scientists on oak health.

In 2001, with several oaks on campus with health issues, we contacted the Santa Clara County Agriculture Extension Services for help identifying causes of symptoms. (Positive identification of Phytophthora ramorum can only be made by certified samplers.) Samples of tissue on the margin of live and dead infected tissue are cultured by a laboratory. All samples taken at Stanford thus far have been negative.

For excellent, up-to-date information about Sudden Oak Death please visit:

»