Eastern Forest Threat Center - Sudden Oak Death
Bleeding canker on infected oak

Bleeding canker on infected oak

USDA Forest Service

Sudden Oak Death
Phytophthora ramorum

A phenomenon known as sudden oak death (SOD) was first reported in 1995 in central coastal California. Since then, tens of thousands of tanoaks, coast live oaks, and California black oaks have been killed by the fungus Phytophthora ramorum.

Keywords: oaks, fungus, pathogen, oak mortality, bleeding canker, leaf spot, twig dieback, leaf discoloration, crown dieback, necrotic bark tissue, SOD

Distribution Map Distribution Source Image

Threat Description

Previously, SOD was known to occur only in California and southwestern Oregon; however, transporting infected hosts may spread the disease to trees and shrubs elsewhere in the U.S. Limited tests show that many oaks are susceptible to the fungus, including northern red oak and pin oak, which are highly susceptible. On oaks and tanoak, the fungus causes a bleeding canker on the stem. The pathogen also infects Rhododendron species, huckleberry, bay laurel, madrone, bigleaf maple, manzanita, and California buckeye. On these hosts, the fungus causes leaf spot and twig dieback. Cankered trees may survive for one to several years, but once crown dieback begins, leaves turn from green to pale yellow to brown within a few weeks. Black or reddish ooze often bleeds from cankers, staining the bark surface and the lichens growing on it. Bleeding ooze may be difficult to see if it has dried or has been washed off by rain, although remnant dark staining is usually present. Necrotic bark tissues surrounded by black zone lines are usually present under affected bark. Because these symptoms can also be caused by other Phytophthora species, laboratory tests must be done to confirm pathogen identity.