Are all four photos of the same plant? None show an azalea. The bottom three seem to be rhododendrons, but the leaf shape of the topmost one is more suggestive of a pieris because of the sharp points at the apex of the leaves. This may, however, be a distortion because of the angle the photo was taken from. In any case, the leaves show the kind of spotting caused by any one of several fungal infections. You can protect the new leaves with a copper based fungicide, but such infections are very unlikely to kill the plant and most people just live with them. Getting rid of the dead leaves once they fall can help, so can pruning out any dead and/or tangled growth.

Thanks. They are all the same plant, my photography skills leave something to be desired...

Is this something likely to spread to other plants if left untreated? My new home came with a rather large, well kept garden, and I find myself a bit over my head trying to keep up with it.

The fungal spores are ever present. Spotting can be worse in some years than in others and some rhododendron varieties are more prone to infection than others. It is a genus specific issue, so will not spread to anything outside the rhododendron family if left untreated. Even dedicated rhododendron lovers generally just accept that there is going to be some spotting and ignore it as much as possible.

Ok, thank you!

I do believe that the shrubs shown here are mountain laurel. The leaf spots are from a fungal disease called macrosphraella colorato. I know, my laurels are afflicted with this. I called up a radio show to discuss this. It was advised that the leaves underneath the plants be raked and disposed of. Also an application of a fungicide (Daconil) about 3 times during the growing season at regular intervals be tried.

The plants will drop the affected leaves. New growth will be fresh and green but will soon succumb and get the spots too. After this year's blooming, I plan to prune off about a third of the bushes. I will continue with the fungicide applications. I live on a mountain and see the same leaf spots on my neighbors' Laurel. Whether they have a stash of fallen leaves at the base of the shrub or are growing in a raked area doesn't seem to matter.

These mountain laurel are native to this area, south Central Pennsylvania, and have been growing here for decades. We built our home here 40+ years ago. The shrubs were lush and healthy. I noticed this leaf blight about 5 ? or so years ago.

I have also noticed that my store bought rhododendrons planted in a nearby area are getting these spots on their leaves.

I don't know if the plants will recover with time and attention, but it is sad to see the once beautiful mountain laurel, the state flower of PA., a shadow of its former self.

The photos certainly could be mountain laurel. Any fungus disease that effects mountain laurel could also infect rhododendrons, pieris, and related plants. Whether this is macrosphraella colorato or another strain of fungus doesn't really matter. The treatment would be the same and as you've discovered, not terribly effective. That the laurels in your area appear to be in decline from this sort of disease is almost certainly related to environmental conditions - increased warmth, rainfall patterns, etc.