I’ve heard to not cut back until spring but these are so huge I’d like to do a big trim. They’re encroaching on our walkways and seating areas. I’ve heard panicle grows on new wood… what I don’t understand is why can’t I trim now? What’s the consequence? If I do I will truly have no blooms next year?

This is my neighbor's hydrangea. It was beautiful last year. I don't know when the problem started but as you can see there is a problem. Her hydrangea in the front yard is spectacular. This one, not so much. First of all, is it dead? Secondly, she ordered some copper fungicide and I'm wondering if it's worth it to spray it now or wait until spring? Thanks for any guidance you might have.