Answer: Rhododendrons are subject to a number of problems, including root rot (causes wilting of leaves), fungal leaf spot (rusty red areas on sections of leaves), and winter damage (mahogany red leaves). Without seeing your rhodies, and based upon the description that the damage is on the top of the shrubs, I'd guess you're dealing with winter damage. Leaves can dry out when the ground is frozen and roots cannot supply replacement water during bright, sunny weather. The affected plant parts won't regain their health so prune them off to encourage healthy new stems and leaves.
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