Brown and red leaves on a rhododendron can be caused by too much fertilizer, too little water or a mulch or soil piled around the top of the roots. I see you have a groundcover on top of the roots so the poor thing is suffocating. You can pull away the creeping Jenny and prune the shrub back after it blooms in the spring and fresh green growth will tell you it has recovered from the problem. These plants do not need fertilizer and like only a very light mulch with a groundcover no closer than 6 inches to the base of the plant. The also like lots of water during dry spells. Keep growing, Marianne Binetti