From the things I’ve read, Immunox is not effective on brown rot shoot blight. I’ve had what I think is pretty bad brown rot shoot blight on my nanking cherries, check out this thread about that:
I did spray some copper on them this weekend since I had mixed a tank for something else, but my main plan is to spray Indar during bloom. In some of the papers linked in that thread, two treatments are recommended with fungicides that have different modes of action. I need to get ahold of something else to spray for it in addition to Indar. I have a small bottle of Indar which I got via a group buy here a couple months ago.