Black fungus on Autumn Monkshood

Hi all! Each year now, a black fungus develops on my Autumn Monkshood. I've tried spraying anti-fungal sprays but it's always too late. What's left are these stumpy things, pictured below. The foliage that remains is gorgeous and the plants are vigourous, so the fungus isn't killing them. But...there are no flowers.
When is should I start spraying them? Thanks in advance and apologies if the pictures aren't clear...vc