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A Disease That’s Felled Forests in California and Oregon Shows up in Washington

A tree disease that’s decimated forests in California has made its way north to western Oregon and Washington.

May 5, 2017

It’s a sunny spring morning at the Bloedel Reserve, a public garden on Puget Sound’s Bainbridge Island. Roads lead to paths lined with blossoming bushes and trees.

Darren Strenge, the reserve’s plant health manager, is showing me the rhododendron glen. That’s where a gardener first spotted a problem back in 2015: a plant that wasn’t healthy.

“Some leaves were dying completely. And a couple of significant branches were dying off,” he recalled.

Strenge took a sample and sent it into a lab. The answer came back: the plant had the pathogen that causes sudden oak death.

The disease has decimated forests in California and infected forests in southwestern Oregon. And now it’s made its way north to western Oregon and Washington, where rhododendrons, Douglas firs, and western larches are most susceptible. It has the potential for such disastrous effects that agencies, scientists, and citizens are working together to try to keep it under control.

A tanoak tree in Northern California's Humboldt County, killed by sudden oak death. Oaks have no natural resistance to the disease, and suffer 100 percent mortality when infected. Courtesy University of California Extension.

Sudden oak death is a water-borne mold called phytophthora ramorum — taken from the ancient Greek expression, plant destroyer.

One species of phytophthora caused the potato famine in Ireland. In California and Southwest Oregon, sudden oak death has felled millions of tanoaks.

“If it’s detected in a forest or a landscape situation where it’s spreading, those areas would go under a quarantine,” he said, “which would have a tremendous economic impact to not only the forest community but also the nursery industry, the timber industry, the Christmas tree industry.”

In California, it has cost an estimated $150 million dollars in lost property values and efforts to control the disease, according to a study that didn’t include the cost of increased fire risk or the loss of ecosystem services.

Gary Chastagner, a plant pathologist at Washington State University's Research and Extension Center in Puyallup. Credit: Eilís O'Neill, KUOW/EarthFix

That’s why the Washington Department of Natural Resources is trying to track its spread across the state.

Early detection is the key to keeping the pathogen from doing the kind of damage to Washington’s forests that it’s done to forests further south. And it’s what eventually saved the Bloedel Reserve, where Navage is pretty sure his team has won the battle. No one here has detected the mold for a year. But, across the western states, people are still on high alert.


The Bloedel Reserve on Washington's Bainbridge Island.