Ligustrum – Spots on leaves (Cercospora)
Q: I planted these three rhododendrons (I thought) a year ago. Now this brown fungus is all over them.
A: I believe these are ligustrum, not rhododendron.
They have a common disease: Cercospora leaf spot.
The good news is that you can bring it under control without a lot of work.
This Clemson factsheet gives details.