Species Facts:

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.

In the United States, Sudden Oak Death is known to occur only along the west coast. However, the fact that widely traded rhododendron ornamentals can be infected with the pathogen and the demonstrated susceptibility of some important eastern oaks make introduction to eastern hardwood forests a significant risk.

Early detection will be important for successful eradication. Oaks defoliated early in the growing season by insects or pathogens may appear dead, but leaves usually reflush later in the season. Canker rots, slime flux, leaf scorch, root diseases, freeze damage, herbicide injury, and other ailments may cause symptoms similar to those caused by P. ramorum. Oak wilt, oak decline, and red oak borer damage are potentially the most confusing.

Portions of this article courtesy of: Pest Alert: Sudden Oak Death
An Oak Tree infected by Sudden Oak Death (Photo from: www.bugwood.org Credit to: Joseph O'Brien)