random header image

Texas Invasive Species Institute

Texas Invasive Species Institute

Sudden Oak Death

Phytophthora ramorum

Class: Oomycetes
Order: Peronosporales
Family: Peronosporaceae

Phytophthora ramorum

Photographer: Joseph O'Brien Affiliation: USDA Forest Service Source: www.bugwood.org Copyright: CC BY-NC 3.0


Sudden oak death is caused by the plant pathogen Phytopathora ramorum. This plant pathogen is also known for causing Ramorum blight in host trees. Sudden oak death has caused a large dieback of several oak tree species in forests from Oregon to California. Ramorum blight has the greatest effect on the leaves and twigs of host plants in forests or nurseries.

Symptoms: Symptoms of sudden oak death can appear as more damaging and severe cankers or less fatal foliar symptoms. If canker-like symptoms appear on the woody portion of the tree, side-effects are very severe and usually result in death of the tree. Cankers weaken the host tree's defense making it vulnerable to further attack from other sapwood fungus (Hypoxylon thourasianum) or woodboring beetles (Buprestidae). If leaves or twigs (foliar) are hosts of sudden oak death, symptoms of leaf spotting or twig die back occur, but the infection typically isn't fatal if the foliar portion of the tree is the host.

Wildland diagnostic guide - provided by Plant Management Network

Host(s): Coast live oak, California black oak, Shreve oak, canyon live oak, California bay laurel, Douglas-fir, and coast redwood, and other tanoak tree species.

Ecological Threat

Sudden oak death is capable of killing large amounts of trees in natural forests which poses the greatest threat to surrounding ecosystems that are dependent on the presence of trees for quality of life. With the removal of a large amount of trees wildlife faces a loss of food sources, the frequency of fires is effected, and soil quality changes with increased runoff of top soil.


The sudden oak death pathogen spreads the most during wet seasons through contaminated plants or soil transferred to home gardens where oak trees are present. The greatest transfer of the pathogen occurs in forested areas with a death toll of over 1 million oak and tanoak trees in the state of California.


Sudden Oak death was first discovered in European nurseries in the 1900's where it spread to nearby countries and was later discovered in the United States in 2001 found on trees in a California nursery.The spread of sudden oak death became severe in 2003 when it spread to forests from California north to Washington and British Columbia.

Native Origin


Current Location

U.S. Present: CA, OR, WA

U.S. Habitat: Wet and cool climates provide the ideal habitat for sudden oak death, which allows it to spread rapidly along the fog belt in California and Oregon. Researchers have identified an indicator of the presence of sudden oak death is often queued by the presence of California bay laurel (Umbellularia californica). Nurseries create microclimates that mimic the desired wet and cool climate preferred by sudden oak death allowing it to spread to trees away from the northwest forests of the United States.


California authorities are currently working to quarantine forested areas and nurseries where sudden oak death pathogens are suspected to be present to prevent further spread. If you live in an area where the pathogen exists, preventitive measures can be taken to oak and tanoak trees by using a phosphonate compound called Agri-Fos, which can be injected directly into the trunk. This is not a cure for sudden oak death, but it can protect trees from contracting the disease, and control further spread if caught in early onset and used properly. Recommended treatment should be applied in the fall or spring with bi-annual treatments of trees that are at the greatest risk for contracting the pathogen.

More information for homeowners - provided by California Oak Mortality Task Force


Davidson, J. M., S. Werres, M. Garbelotto, E. M. Hansen, D. M. Rizzo, and FS USDA. 2003. Sudden oak death and associated diseases caused by Phytophthora ramorum. Plant Health Progress

Goheen, E. M., E. M. Hansen, A. Kanaskie, M. G. McWilliams, N. Osterbauer, and W. Sutton. 2002. Sudden oak death caused by Phytophthora ramorum in Oregon. Plant Disease 86(4):441.

Guo, Qinghua, Maggi Kelly, and Catherine H. Graham. 2005. Support vector machines for predicting distribution of Sudden Oak Death in California. Ecological Modeling 182(1):75-90.

Harmon, Philip F., and Carrie L. Harmon. 2004. Sudden Oak Death. Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. PP197 http://edis.ifas.ufl.edu.

Rizzo, David M., and Matteo Garbelotto. 2003. Sudden oak death: endangering California and Oregon ecosystems. Frontiers in Ecology and the Environment 1:197-204.

A Guide for Recreational Users: Simple Precautions to Prevent the Spread of Sudden Oak Death provided by the California Oak Mortality Task Force

Woodward, Susan L., and Joyce Ann. Quinn. 2011. Sudden Oak Death. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood. 25-28. Print.


Internet Sources



< Back to Inventory