Answer: From your description I'd guess Spider Mites have infested your Yew. These tiny little creatures are often hard to spot but the webbing they leave is a give-away. Spider Mites like hot, dry conditions, which are also favored by your Yew. Try washing the plant off with a strong stream of water from the hose to dislodge the insects. Repeat at 2-3 day intervals for a week or two. To prevent future attacks, hose your plant off occasionally or mist the leaves to increase humidity around the plant.
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