Sudden oak death

Phytophthora ramorum
Canker on an infected oak
Scientific classification
Domain:	Eukaryota
(unranked):	SAR
Superphylum:	Heterokonta
Class:	Oomycetes
Order:	Pythiales
Family:	Pythiaceae
Genus:	Phytophthora
Species:	P. ramorum
Binomial name
Phytophthora ramorum Werres et al. 2001

Phytophthora ramorum is the oomycete plant pathogen known to cause the disease sudden oak death (SOD). The disease kills oak and other species of trees and has had devastating effects on the oak populations in California and Oregon, as well as being present in Europe. Symptoms include bleeding cankers on the tree's trunk and dieback of the foliage, in many cases eventually leading to the death of the tree.

P. ramorum also infects a great number of other plant species, significantly woody ornamentals such as Rhododendron, Viburnum, and Pieris, causing foliar symptoms known as ramorum dieback or ramorum blight. Such plants can act as a source of for new infections, with the pathogen-producing spores that can be transmitted by rainsplash and rainwater.

P. ramorum was first reported in 1995, and the origins of the pathogen are still unclear, but most evidence suggests it was repeatedly introduced as an exotic species. Very few control mechanisms exist for the disease, and they rely upon early detection and proper disposal of infected plant material.

The disease is known to exist in California's coastal region between Big Sur (in Monterey County) and southern Humboldt County. It is confirmed to exist in all coastal counties in this range, as well as in all immediately inland counties from Santa Clara County north to Lake County. It has not been found east of the California Coast Ranges, however. It was reported in Curry County, Oregon (just north of the California border), in 2001. Sonoma County has been hit hardest, having more than twice the area of new mortality of any other county in California.

...
Wikipedia