All my Lantanas have this blight on their leaves. What is causing it and how can I cure it?
Your location isn't in your profile - adding it will help folks help you.
My best guess is entomosporium, especially if you get the leaves wet when watering, or live where it rains a lot. I can't find a good reference, but see this GardenWeb post, especially the photo. Of course, bear in mind that this is just another forum.