Answer: Boxwoods are reliably insect and disease resistant so I wonder if the yellow spots are on the oldest leaves. It's normal for evergreens to drop their oldest leaves (those toward the center of the plant) in favor of replacing them with healthy new foliage. This is an annual event and nothing to worry about. The leaves will turn completely yellow and then drop off. Later this summer you'll find brand new leaves where the old ones were.
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