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Plant Pathology

Department of Plant Pathology


Impact Stories

Sudden Oak Death - A Threat to Forests and Landscapes

OARDC scientists are devising strategies to manage the spread of Sudden Oak Death (SOD), an invasive and potentially lethal disease of oaks and dozens of other plants, including common landscape ornamentals.


Sudden Oak Death is an aggressive and potentially lethal disease of oaks and dozens of other plants and caused by the pathogen, Phytophthora ramorum.  First detected in California in the mid-1990s, Sudden Oak Death has moved into forests in California and southwestern Oregon. Because oak is a predominant species in North American forests, the loss of oak trees can dramatically alter forests and landscapes.

Across the United States, the economic threat of Sudden Oak Death to oak forest commercial timber production is estimated as being over $30 billion.  In Ohio forests, oaks comprise 10 billion board feet, or 25% of the total tree volume; this is the largest percentage of any other genus.

Red oaks, including northern red oak, are known to be susceptible to P. ramorum. Sudden Oak Death also has the potential to impact Ohio’s ornamental industry, which is a significant component of the state’s economy (more than $615 million in 2004 alone).

There are many unanswered questions about Sudden Oak Death and how to manage or stop its spread.


Scientists have identified several compounds in coast live oaks that inhibit the growth of P. ramorum, the Sudden Oak Death pathogen, which are associated with host resistance. OARDC scientists are now studying how these compounds could be used to identify resistant trees ahead of the infection front so that they can be protected from urban development, logging, or fire.


Understanding Sudden Oak Death will help scientists learn more about how plants resist or fight infection and guide the development of management strategies to stop this devastating threat to North American forests.  In many cases the best management approach may not involve eradication of oaks or other host plants, but to allow the proportion of coast live oak population that is resistant to evolve into more stable stands.

The economic impact can therefore be significant if unwarranted management approaches, such as elimination of susceptible trees and replanting with resistant trees, are avoided.  Knowledge that we gain in the California studies will be invaluable in devising management approaches if the disease invades the Eastern oak forests.

Pierluigi Bonello and Anna Conrad, Department of Plant Pathology; David L. Wood, Dept. of Environmental Science, Policy, and Management, University of California, Berkeley.