Posted: 29/07/2016 at 18:52
I went and looked at mine, just Sorbus aria, not a cultivar. One is in the same state as yours, I mowed more leaves than grass later on. The other 2 are fine.
It's not a disease or an infestation and I wouldn't consider using something that kills indiscriminately in my garden. Everyone to his own choices but you might like to think about what a 'bug' is and which beneficial 'bugs' are now dead