Peronosporales: Pythiaceae:
Phytophthora ramorum Werres et al.

A disease-causing oak mortality was first discovered in California in 1995. Termed sudden oak death, it was later determined that the causal agent was a newly described fungal pathogen, Phytophthora ramorum. After its initial detection, sudden oak death was only thought to be established in California and Oregon. However, further research revealed that the new pathogen makes use of multiple hosts including various species of Rhododendron, Kalmia, and Viburnum which are heavily traded in the nursery industry. Nationwide surveys have identified positive samples of P. ramorum in several additional states. To date, only one sample from Pennsylvania has tested positive for the fungus. The positive sample was from a bonsai plant, which was intercepted in southeastern Pennsylvania, and had no contact outside of its point of sale. This destructive pathogen has grown to epidemic proportions in California, and has the potential to severely affect the oak component of Pennsylvania's forests.

The Bureau of Forestry participates in a multi-agency effort to detect and control this invasive threat since 2003. To date, only one sample from a nursery site in Delaware County has tested positive for P. ramorum. Infected plant materials at the site were destroyed and additional surveillance was implemented.

Sudden oak death can be recognized by crown dieback, leaf discoloration, or the presence of black or red ooze bleeding from cankers on the bark. Removal of diseased bark will reveal necrotic tissue surrounded by black zone lines. Homeowners can help to stop the spread of sudden oak death by landscaping with native plants.

To report possible infected forestland trees in Pennsylvania, contact:
The Bureau of Forestry, Division of Forest Pest Management (717) 948-3941
For more information about sudden oak death in Pennsylvania, contact:
The Pennsylvania Department of Agriculture

Return to Invasive Threats Home