Answer: Perhaps the holly isn't getting enough iron. Signs of iron deficiency include: new leaves are all yellow except for the veins; older leaves are yellow on the edges. It could be that the dry weather is affecting the shrub's ability to take up nutrients. Holly prefers a slightly acidic (6.0-6.5 pH) soil, and though they are drought tolerant, do best if the soil isn't allowed to dry out. You may be able to reverse the yellowing by feeding the holly with a foliar fertilizer that contains iron, and add a fertilizer, like Hollytone, to the soil as directed on the label.
It the leaves are stippled with yellow, mites are the likely culprit. They thrive in dry weather. Inspect the undersides of leaves for the tiny creatures (you may need a magnifying glass). If you find the eight-legged mites, spray with an insecticidal soap or a light horticultural oil as directed on the label. Hope this helps!
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