I have a mature bronze fennel that seems to have some type of foliar disease that has caused the whole plant to kind of shrivel. It looks ok from far away, but when you get close, you can see the mottling and disfiguration of the leaves and I've yet to have a single flower umbel make it out of the papery sheaths of the leaves. My searching turns up a leaf blight caused by Cercosporidium punctum. Apparently only dill and fennel relatives get this. I've never seen it before and I see no suggestions for treatment organically. Any suggestions?