||In the mid-1990s, hikers in Marin County, CA noticed tanoaks (Lithocarpus densiflorus) were dying. The canopies of these trees appeared to turn brown in a matter of weeks, so people called the phenomenon “sudden oak death.”
Photo by Marin County Fire Department.
The disease was first observed in 1993 in Germany and The Netherlands on Rhododendron and Viburnum. In the United States, Phytophthora ramorum was first detected in California on oaks and tanoak in the mid-1990s.
The source of Phytophthora ramorum is unknown but we do
know that United States forms of this pathogen did not come from Europe.
mid-1990s, there were no reports of this species in the United States or Europe.