Scientists: Bark disease found on maple trees in Tacoma can also harm people

Washington is known for its abundance of green trees, but now, a disease has been discovered in the South Sound attacking maple trees. Scientists know it as Sooty Bark Disease and say it can injure people too.

Sooty Bark Disease was spotted at Franklin Park in Tacoma while a researcher with Washington State University Puyallup Extension was visiting the park. Experts said it comes from a fungus that has been in the Pacific Northwest environment.

"The working theory is the fungus that causes Sooty Bark Disease has been around in the Pacific Northwest for the last 50 years or so. But it wasn’t causing a problem because the climatic conditions were keeping its population downn, or keeping trees healthy enough that they can fend it off and you would never even see that there is a problem there," said Ben Thompson, with Washington State Department of Natural Resources.

Scientists will be working to determine if the extremely hot temperatures seen this summer and in recent years are what caused the fungus to become harmful and spread. Experts explained the fungus gets into trees and creates a dark powdery lesion on the outside of bark that looks like soot.

"But then it could get beneath the bark into the actively growing tissues of the tree and that’s where it starts to interrupt flow of water and nutrients between the roots and the canopy," said Thompson.

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Thompson said the state became aware of the infected maple trees after the WSU researcher notified them of his findings in Tacoma.

Scientists explained spores from the fungus can be an irritant to the lungs. Thompson said there is a low risk of injury if people are near an infected tree or just walking by.

"The people that are at highest risk for that kind of exposure are the folks doing tree work because they’re actually out handling the trees, they’re climbing the trees, they’re cutting on the trees. If they threw, for example, infected plant materials through a wood chipper, all those spores would get kicked up and they’re right there breathing it all in," said Thompson.

Thompson said there is research about Sooty Bark Disease in eastern states in the U.S. and in Europe, but there is none in the Pacific Northwest.

"Until we have some baseline research to tell us about what this disease is and how it operates in the Pacific Northwest, then it’s going to be harder for us to evaluate if things are changing over time," said Thompson.

Washington will be one of the first in the region to study Sooty Bark Disease. The DNR awarded WSU Puyallup Extension a $40,000 grant to lead the research with the help of citizen scientists. WSU also provided a grant for the study.

"Engaging the community and getting folks out there to teach them how to recognize the signs and symptoms of Sooty Bark Disease, and how to record that information across different locations in the city where there are different heat gradients—so where there are cooler places, where there are hotter places, where there are some spots in between," said Thompson.

Forest Health Watch has a website for community scientist interested in participating in the study.