Answer: You didn't indicate whether these yews were recently planted or not. If so, you'll have to consider how the plantings were made. Was the soil well prepared? They need well drained soil, and prefer a pH that is neutral to slightly acidic. Did they receive proper care after planting, including proper watering to establish their root system?
If they are an established planting, what has changed that could be causing their problems? Yews are considered one of the most carefree of evergreens, but one thing they cannot tolerate is "wet feet." Did you receive an inordinate rainfall last summer/fall? Is drainage in the area good? On the other hand, did they go into the winter with less than adequate water (an inch of water a week is recommended)? Although there are a few insects that could cause a problem, you have not mentioned any bugs, and cultural problems are far more common.
Consider the situations presented above and you should find the key to correcting the problem. Yews are a pretty hardy lot, and may come out of it if the problems is corrected. If these suggestions don't seem to help, contact your County Extension Service (ph# 728-1581) for further assistance.
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