Answer: Since yews are evergreen shrubs, and evergreens eventually lose their oldest leaves (which are replaced in time), yellowing and dropping foliage is perfectly normal. So, if the oldest leaves are affected, it's nothing to worry about. If the new growth is yellowing, there is a definite problem, although to diagnose it long distance would be impossible. I'd suggest you take a sample of an affected plant to your local Cooperative Extension office or Master Gardener Plant Diagnostic Clinic for positive identification. Contact King County Cooperative Extension (206-296-3900) for clinic locations nearest you. Best wishes with your yews.
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