Forest Health: Sudden Oak Death

Oak mortality is caused by a new pathogen, Phytophthora ramorum

A phenomenon known as Sudden Oak Death was first reported in 1995 in central coastal California. Since then, tens of thousands of tanoaks (Lithocarpus densiflorus), coast live oaks (Quercus agrifolia), and California black oaks (Quercus kelloggii) have been killed by a newly identified fungus, Phytophthora ramorum. On these hosts, the fungus causes a bleeding canker on the stem. The pathogen also infects Rhododendron spp., huckleberry (Vaccinium ovatum), bay laurel (Umbellularia californica), madrone (Arbutus menziesii), bigleaf maple (Acer macrophyllum), manzanita (Arctostaphylos manzanita), and California buckeye (Aesculus californica). On these hosts the fungus causes leaf spot and twig dieback.

As of January 2002, the disease was known to occur only in California and southwestern Oregon; however, transporting infected hosts may spread the disease. The pathogen has the potential to infect oaks and other trees and shrubs elsewhere in the United States. Limited tests show that many oaks are susceptible to the fungus, including northern red oak and pin oak, which are highly susceptible.

Sudden Oak Death Pest Alert

Plant Protection and Quarantine Sudden Oak Death

Insect Threats

Chestnut Borer | Gypsy Moth | Hemlock Woolly Aldegid | Southern Pine Beetle

Other Forest Health Topics

Four Threats to Forest Health | Forest Health Initiative | Red cockaded woodpecker | Invasive Species | Prescribed Burning

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Last Updated: July 27, 2009