Non fruiting soursop

Jpiercen27 starts with ...
I have had a soursop growing for the last 7 or 8 years and although it grows vigorously, it has never set a single fruit. It flowers over and over but the fruits drop off when they are the size of a walnut. I have added all sorts of mineral supplements and fertiliser over the years, thinking that it might be some sort of deficiency, but to no avail. I was wondering if it is anthracnose as a lot of the flowers have black marks as per photos. I have issues with anthracnose on other ammonias in my yard but usually you can expect to get a couple of fruit even on an infected tree. Just about ready to pull it out and start again. Any help would be appreciated thanks

Pictures - Click to enlarge
Picture: 1