I'm assuming you are experiencing the same wet, late, cool spring in NY that we are here in Maine. These conditions are perfect for the spread of various leaf spot fungal diseases on rhododendrons and other plants. There are many possible culprits, all of which are more unsightly than they are a serious threat to the survival of the plant. Clean up any fallen leaves, make sure the plant receives good care over the summer and pray for some sun.

If you really want to try a fungicide, there are several wide spectrum ones such as Benlate which may help. Not really necessary, though.

Thanks. Oddly, though, this plant is the only one of mine to be suffering from this and it's the one that gets the best ventilation and sun. The picture was taken during our only dry spell about ten days ago. I'll probably just keep an eye on it. Also, oddly, I first saw a Flame Azalea in Maine, of all places, a couple of decades ago at the entrance to Wolfe's Neck state park north of Portland. The ranger had no idea where it had come from, and we figured somebody had planted it there. It inspired me to grow native azaleas. Here's a picture of my flower.

Here is a link that might be useful: Flame Azalea flower

The flame azalea is Rhododendron calendulaceum. It is occasionally affected by Rhododendron Leaf Spot. The University of Massachusetts has a good web page on the fungus Cercospora handelii, Colletotrichum azaleae, and Pestalotiopsis sydowiana, fungi that can cause leaf spots on rhododendron and azalea

Here is a link that might be useful: Rhododendron Leaf Spot