rhododendron bush sick
I had some local Master Gardeners visit my property recently and they informed me that my bush was looking stressed and gave me your contact info. The leafs are faded and there are small spots on the under leaf. Please Instruct on how to help my bush.
We agree that your shrub is not happy.
The main issue that we see- the yellowing/stippled leaves and the yuck on the back of the leaf looks like evidence of lace bugs, which are plant sucking insects.
Here is our page on them and their control: https://extension.umd.edu/hgic/topics/lace-bugs-trees-shubs
They are more likely to be a problem on rhododendrons and azaleas grown in full sun, which is not their preference. We are not sure yours is in full sun, but it definitely is a stressful, hot spot surrounded by asphalt, pavers and wall.
Under best conditions, in a part-shade spot with minimal pesticide use and a diversity of plant material, beneficial insects in the landscape keep them in check.