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Douglas firs turning brownish red and needles dying might look like Swiss needle cast. But forestry expert Jim Reeb of OSU Extension thinks that most of the problems this year are drought related. When trees are stressed, insects and disease can more easily attack the trees.
(Oregon State University)
When there are no peas in the pods or flowers on the dahlias, get the answers you need with Ask an Expert, an online question-and-answer tool from Oregon State University's Extension Service.
OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website and type in a question and the county where you live.
Here are some questions asked by other gardeners. What's yours?
Q: I have recently noticed many local Douglas firs turning brownish red (many needles dying), with some trees having entire limbs apparently dead or dying. I've seen this here in Corvallis, in the Coast Range, in the Portland area and in the Columbia Gorge; and I have seen it in young forest stands (20+ years) as well as individual 100-year-old trees on urban city lots. An arborist in Portland diagnosed one of these older trees as Swiss needle cast. What is going on? Will the trees die? Is there treatment possible? - Benton County
A: We think that most of the problems this year are drought related. When trees are stressed, insects and disease can more easily attack the trees. I spoke with our Dave Shaw, an Extension forest health specialist. He recommended that you look at the following articles:
- Many Douglas-fir with dead tops and branches in the Willamette Valley this year
- Dead branches, dead tops and dead trees: The interaction of water stress, insects and disease
-- Jim Reeb, forestry, OSU Extension
Q: I have a quarter-acre plot of land now covered with tall grass. It is just below the tree line on the side of a hill. Soil is basically brown clay with broken shale at about 2 feet down. I want to know when doing site preparation what a reasonable maximum slope is for organic gardening. I am familiar with using 2-by-12 boards for perpendicular soil stabilization in the terracing process, but would like to know what slope would allow me to garden without going the terracing route. Thanks in advance for any light you can shed on this issue. - Douglas County
A: If you intend to till the soil to work in organic matter on a yearly basis, you will get erosion on any plot with a slope greater than 15 percent to 20 percent. By leaving sod strips between your planted sections you can limit the erosion potential. If you go with what some gardeners call a lasagna garden where organic materials are layered over the soil, it will help to control the erosion a lot. If the site is quite steep you may have to terrace to create walking and working spaces for good footing. -- Steve Renquist, OSU Extension horticulturist
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