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

May 5, 2017

A disease commonly known as “sudden oak death” has decimated forests in California and infected forests in Oregon. And now it’s made its way north to Washington where rhododendrons, douglas firs, and western larches are most susceptible. It has the potential for disastrous effects.

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

It was in the rhododendron glen  that a gardener first spotted the problem. Back in 2015, he noticed a plant that wasn’t healthy, remembers plant health manager Darren Strenge.

"Some leaves were dying completely," Strenge says. "And a couple of significant branches were dying off."

So Strenge took a sample and sent it into a lab. The answer came back: the plant had the pathogen that causes sudden oak death. It’s a water-borne mold called phytophthora ramorum.

"Phytophthora in ancient Greek translates as plant destroyer," Strenge says.

One species of phytophthora caused the potato famine in Ireland. In California and Southwest Oregon, sudden oak death has felled millions of tanoaks. Western Washington and much of western Oregon don’t have tanoaks, but they do have the cool, wet climate the water mold loves, and they also have hundreds of plants that are susceptible to infection. That’s why the USDA descended on the Bloedel Reserve just weeks after the mold was found. They found it at fourteen sites throughout the garden, Navage says.

"Right from the get-go it seemed fairly hopeless," Navage says. "You have a mandatory destruction zone of two meters, so the potential was that everything around you that you see would have to be destroyed. It instills fear and anxiety. It would be hundreds of thousands of dollars to mitigate this garden space."

Navage and his team set to work pulling plants out of the fourteen sites, steaming the soil to kill the mold, and rebuilding paths to change the way water moves around the garden.

The mold was detected early here, because gardeners are constantly checking on the plants, but, in the wild, it could spread fast. So far, it’s been detected in forty-five nurseries whose stock includes infected plants brought in from California, Oregon, or British Columbia, and it’s been found in streams and rivers up and down the I-5 corridor and in the Dungeness River out on the Olympic Peninsula.

In plants other than tanoak, the water mold doesn’t kill the plant but rather some of its leaves and shoots and sometimes its branches. But that’s still a huge problem, says Gary Chastagner, at Washington State University.

"If it’s detected in a forest or a landscape situation where it’s spreading, those areas would go under a quarantine, 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," Chastagner says.

In California, it has cost an estimated one hundred fifty 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.

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 Andy Navage is pretty sure they've won.

At the Bloedel Reserve, no one’s detected the mold for a year. But, across the Western states, people are still on high alert.

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