Is it Black Vine weevil damage? I've tried using that Bayer Tree and Shrub control with Merit this spring. But looks like some are coming back again! Grrrrr... It's on my Crow's Feather Tiarellas. Any ideas on how to control? What a pain this is! It makes the tiarellas look sick all summer long.
This is what the book by Dan Heims said; Darks Spots on leaves with yellow halo are evidence of infection by the pathogen Xanthomonas.
Remove affected foliage and copper sprays or copper sulfate will help minimize problems. I have removed about an inch of soil around plant and added new also.
I have decided that it looks like a bacterial leaf spot, maybe the one you said. I shovel pruned just the one and have replanted a dianthus raspberry surprise in it's place. We'll see how that goes... gulp :) The other two tiarella's appear fine and I am keeping those. Thankgod it's only one plant!