ASTORIA - A disease native to the Pacific Northwest, once considered a minor problem in young forest trees, is becoming more evident among both younger and older Douglas-fir trees of the Oregon Coast.
Since the 1920's this fungal disease, called Swiss needle cast, has caused severe damage to Douglas-fir planted in non-native locations such as the eastern United States, Europe and New Zealand, according to Katy Kavanagh, a forestry agent for the Oregon State University Extension Service.
"We're not sure what has changed, but it has become more damaging and is killing many of the younger Douglas-fir trees located along the Oregon coast," said Kavanagh.
A discoloration of trees caused by Swiss needle cast was observed in an aerial survey by the Oregon Department of Forestry, with the problem centered around Tillamook but extending from Clatsop County to Curry County.
"It probably continues south into California and north into Washington, said Kavanagh, "but they didn't fly those areas in the survey."
Almost all discoloration from Swiss needle cast is within 14 miles of the Oregon Coast, she said.
The disease is called Swiss needle cast not because it is from Switzerland but because that is where it was first recognized. It makes a tree look as if it is going bald.
Normally a conifer tree keeps four years worth of needles on a branch. But following infection, Kavanagh said, the tree sheds the older needles, leaving only one to two years of growth.
Spores that spread the disease are released by older needles in the spring, infecting new growth, she added. The damp conditions typical in Pacific Northwest springs help spread the disease.
"There is still a lot we don't know," said Kavanagh. "We don't understand why one tree gets it and others don't, or why some trees survive an early attack and are able to continue to thrive.
"Currently," she said, "the Oregon Department of Forestry and Oregon State University are conducting research to identify how extensive the disease is and if there are trees that are more resistant."
Some foresters have controlled the disease by planting resistant trees and avoiding planting Douglas-fir in high-risk sites, according to Kavanagh. Applying fungicides in forests is not a viable control method, she said. They would have to be reapplied after every spring rain.
Christmas tree growers around Oregon have dealt with the disease for many years, Kavanagh said, because they sometimes use seed from infected areas. They spray their trees with a fungicide.
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Katy Kavanagh, 503-325-8573