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Sudden oak death

Sudden oak death is still poorly understood and only known to be present in the far western United States.


Sudden oak death in North America

Sudden oak death was first seen in Marin County, California (north of San Francisco) in 1995, when thousands of oaks were found to be dead or dying from an unidentified cause. In 2000 Phytophthora ramorum, a fungus-like organism, was determined to be the cause of sudden oak death. Currently in the United States, the disease is known to occur along the coast of California and southern Oregon.

Outside of North America

Phytophthora ramorum is also found in a number of European countries, but until 2003 the pathogen had only been found on ornamental plants such as rhododendrons and viburnums. That year, infected oaks (including southern red oak and northern red oak, both native to North America) were found in southwest England and the Netherlands. All of these infected trees were nearby infected rhododendrons.


Don’t move P. ramorum to new sites

Several years ago, P. ramorum was accidentally moved from nurseries in California to at least 21 other states by shipping infected plants. However, surveys did not find it naturally in these states and the infected plants were destroyed. Quarantine restrictions (laws to keep harmful plants and diseases from moving beyond where we already know them to be) prevent future shipments of infected plants.

Phytophthora ramorum is classified a prohibited species in Wisconsin under Chapter NR40.

Last revised: Tuesday September 04 2018