Sudden Oak Death

For the past twenty years, oaks in Northern California have been under siege from a plant pathogen called Phytophthora ramorum, commonly referred to as Sudden Oak Death (SOD). P. ramorum produces spores that are dispersed through the air or water, or carried by people, animals, plants, soil, and equipment. The ideal condition for P. ramorum is warm (68 degrees) and moist, making riparian woodlands especially susceptible. Coastal counties from Humboldt to Monterey have been especially hard hit.

Forest near Big Sur, California showing symptoms of Sudden Oak Death.
Photo by Hemhem20X6 (released into the public domain, by the author),

Symptoms include cankers on the trunk or limbs of a tree; and rapid leaf or canopy death over a two to three week period. Quercus agrifolia and Q. kelloggii oaks have a high mortality rate. Other woody plants in the plant community may be hosts to the disease—including rhododendron, California bay laurel, madrone, Manzanita, redwood, coffeeberry, and California buckeye. The pathogen is not native, and may have been introduced through an imported ornamental plant, possibly from Asia. So far there is no known cure; infestations should be reported for diagnosis, since other diseases have similar symptoms.

The California Oak Mortality Task Force was assembled in 2000 to address the pathogen and its affects, and to coordinate with other agencies, universities, and other private and public groups. Several websites provide information: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74151.html, www.suddenoakdeath.org, and www.na.fs.fed.us/SOD.