Septoria is also known as angular leaf spot because of the shape of the lesions. In this case, they seem to be circular. There many causal agents for leaf spotting in azaleas and rhododendrons. Wetter than average weather encourges fungal infection. A broad spectrum fungicide such as daconil applied now may or may not help, but most azalea and rhododendron growers learn to live with the spotting unless it becomes very serious. Your county extension service can identify this particular infection and recommend a treatment, but the spotting really doesn't look terribly serious at this point.

It's on the older leaves. The new growth will hide it in a few weeks and eventually the old leaves will be shed. It's a cosmetic issue rather than a serious health problem.

Thanks for the information from both of you. We had a wet spring and hot, dry summer last year and looks like we are going to have the same thing this year.