Washington State University

WSU Sudden Oak Death Program

What is Sudden Oak Death?

Sudden Oak Death is the common name for a disease caused by Phytophthora ramorum, a previously unknown and exotic plant pathogen. SOD symptoms on nursery stock

  • P. ramorum is currently only known to occur in 14 counties in California, a small area in southwestern Oregon and several European countries.
  • P. ramorum has killed hundreds of thousands of oak and tanoak trees in California.
  • P. ramorum spreads aerially through forest landscapes by wind and wind-driven rain.
  • P. ramorum survives in infested plant material, litter, soil, and water and can be moved long distances in nursery stock.

This pathogen can infect a large number of plants including Douglas-fir, grand fir, rhododendron, viburnum, big leaf maple, vine maple, madrone, Pacific yew, salal, and other tree, shrub, and herbaceous plant species in Washington's natural and urban landscapes, and new host species are being added continually. While the pathogen can cause dramatic symptoms and death in tanoak and some oak species, on many hosts the organism causes only minor symptoms, usually foliar or stem blights. The similarity of P. ramorum symptoms to those of other plant diseases makes identification difficult.

Does Sudden Oak Death Pose a Threat to Washington?

Western Washington is a "high risk" area for diseases caused by P. ramorum because of favorable environmental conditions and the abundance of susceptible host plants.

P. ramorum has been detected in more than 33 western Washington nursery sites since the summer of 2003, but so far eradication efforts appear to have prevented its spread to plants in Washington's forest and urban landscapes. However, the recent detection of P. ramorum in a stream associated with an infested nursery illustrates the potential for this organism to spread from nurseries into Washington's natural and urban landscape. While the ecological impacts of P. ramorum in Washington are unknown, the spread of this pathogen to plants in our forest or urban landscapes would trigger a series of quarantines for Washington's horticulture and forestry products. In addition, the destruction of infected plant material in nurseries to eradicate P. ramorum and prevent its further spread has already caused millions of dollars in losses to the nursery industry in Washington, Oregon, and California.

What's new:

Stream monitoring pilot study


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Contact: Gary Chastagner, 253-445-4528 | WSU Puyallup Research & Extension Center,2606 West Pioneer, Puyallup, WA, 98371-4998 USA