We purchased a Crusader Hawthorn tree last year. It seems to have lots of growths\bumps all over the green fruit berries & when touched they crush to an orange powder. I’ve been trying to search online & think it might be hawthorn rust. It doesn’t seem to be on the leaves. We have lost leaves as well. I don’t really see much treatment listed. I just am questioning how to know it’s rust & if I need to do anything to treat it this year or next spring.
Rust can be somewhat common especially when the weather conditions are right. Nothing you can do at this stage besides collect leaves and fruit that drops and pitch it out. You can spray as a preventative next spring starting at bud break repeating 3-4 times based on the label -use Sulfur, Mancozeb or Bonide’s Fungonil. Take samples to local garden store for someone to see and possibly identify. But what you’re describing sounds like one of the rusts.