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Douglas firs in Western Oregon stressed from wet weather
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February 19, 2003
CORVALLIS - Have you noticed Douglas fir trees turning reddish-brown and dying around the Willamette Valley, Coast Range, or foothills of the Cascades?
These Douglas fir trees are suffering from last year's wet weather, according to Oregon State University Extension forester Brad Withrow-Robinson.
"Unfortunately, young, dying Doug firs are a common sight up and down the Willamette Valley and in the foothills of both the Coast Range and the Cascades," said Withrow-Robinson.
"In most of the cases I have examined, the cause is quite clearly related to weather - last year's weather," he said. "We had a wet spring last year that caused some trees in low-lying areas and poorly-drained sites to drown. This was followed by a very long dry period in which many young trees simply ran out of water, especially on dry or south-facing sites.
"We got many calls about these symptoms last fall, but it appears some trees that were damaged or killed last year did not show symptoms or die until this spring.
"I think we can expect to see symptoms continue to show up all year," Withrow-Robinson added. "In addition, we will likely see some secondary insect problems that may attack weak trees. A good example might be twig weevils. They are always around and attack individual branches.
Healthy trees produce lots of fragrant pitch to fend off such attacks, but weak trees are less able to 'pitch out' a pest, Withrow-Robinson pointed out.
"As a result, we may see more signs of this common insect than usually as a result of, rather than a cause of, low tree vigor," he said. "Usually there is nothing to be done to save a tree in this situation. So in most cases, the best solution is to replace the tree with another of a different species, such as the Valley ponderosa pine, which is better adapted to some of the extreme weather or site conditions."
Source: Brad Withrow-Robinson