Sudden Oak Death FAQs

What is Sudden Oak Death (SOD)?

Sudden Oak Death is a forest disease caused by the water mold pathogen Phytophthora ramorum (P. ramorum).

Where was SOD First Found in the United States?

Sudden oak death was first detected in the San Francisco Bay Area in 1993. It spread to a forest in Southwest Oregon in 2001.

Where is Sudden Oak Death Currently Found in the United States?

Sudden oak death is found in California and Oregon. For a map showing states with current quarantines and high risk areas, visit the Pest Tracker.

What Types of Plants Does P. ramorum Infest?

More than 75 plant species and cultivars representing more than 45 genera can either be infected by P. ramorum or facilitate its spread. Known susceptible plants include tanoak, coast live oak, California black oak, canyon live oak and sometimes madrone.

How Does P. ramorum Spread?

P. ramorum naturally thrives in cool, wet climates, including plant nurseries that favor these climate conditions. It can spread through wind-blown rain, contaminated irrigation water and infected plants. Soil or potting mix may also spread the pathogen, and it may spread in other ways we do not yet know.

What are the Symptoms of Infection?

There are three disease symptoms – bark cankers, leaf spots and twig dieback. On oaks and tanoaks, infection that results in tissue death and the formation of calluses on the woody portions of the tree are referred to as cankers. Cankered trees may survive several years.

What Kind of Damage Can P. ramorum Cause?

Possible ecological threats include a change in species composition in infested forests and therefore, in ecosystem functioning; loss of food sources for wildlife; a change in fire frequency or intensity; and decreased water quality due to an increase in exposed soil surfaces.

What Quarantine and Regulations Are in Place for SOD?

For information on the current SOD quarantines and federal P. ramorum nursery regulations, visit Or, you can see the Pest Tracker for a general overview of the federal quarantines and high risk areas.