My 5 meters tall apple tree still produced apples 3 years back. But for last 2 years, there were no apple I can keep the doctor away. Although she did bear fruits, but the fruits either got black spots or got lumps on the them. When you saw it, it will make you feel sick actually.

I think she did not feel good so I applied some solutions to it. But she still looks very sick as today. Here are the symptoms I observed.
1. 2 out of the 3 main trunks, it lost significant portion of tree barks. See pictures.
2. A lot of moss grow on the tree trunk and branches. I think there are fungi on branches as well. See pictures.
3. Around 10% of new leaves started have holes on them and some even started turning yellow.
Here were the solutions I tried to get her back to normal for the last 2 years. But it sounds I was not on the right direction.
1. I applied Scotts Bug-B-Gon Insecticidal Soap. Tree barks started falling significantly.
2. I tried Dormant Spray Kit . I applied both Lime Sulphur and Horticultural Oil according to the instruction last year. But fruits became worse.
I want to be smarter this year. So my question are:
a) Are these caused by 1 root cause? Or multiple root causes?
b) What are the best solution to get her back to it's normal and give us the fruit to keep the doctor away.
Thanks to the tree doctors.
New gardener need redemption.