Sudden Oak Death

The origin of sudden oak death (Phytophthora ramorum) is uncertain, but it appeared on the west coast of the U.S. in the mid 1990s.

The pathogen weakens the oak tree, causing reddish or black bleeding ooze from lesions on the bark, and later a rapid browning of the leaves. It renders the tree vulnerable to bark beetle and fungus invasions.1

Many plant species can host the sudden oak death pathogen without dying, including forest trees and shrubs such as mountain laurel, azaleas, rhododendrons, viburnums, witch hazel, and feathery false lily-of-the-valley, as well as ornamental plants.2 Unfortunately, this creates an ongoing source for the air-borne pathogen.3

Hikers, researchers, and horses may unintentionally move spores from one forest to another, unless care is taken to clean their shoes, hooves, tires, equipment, etc. when leaving an infected area, especially in areas of muddy soil.

Various chemical treatments, including injections to the tree trunk, can be used preventatively in an area known to be at risk of an epidemic, or with very early detection. Laboratory tests show northern red oak and southern red oak to be highly susceptible to the disease.4