Gahh I hope it is not what Got all mine this year!!
I have lost numerous plants this year doe to what I think was fungus infections
Maples, Azaleas, Banksia, Privet, Eucalyptus, Pine,.
The first one started mid spring, and just wilted at the top and worked its way down the trunk over a period of a week.
the floliage sagged and then the branches turned black
I sprayed everything with a fungicide but every few weeks I lost another the same way. It affected different trees, and did not matter whether in My diatomite, Akadama, or Rays own mix. Watering was consistent across all trees and none of the deceased were over wet or potbound, or dried out..
Hope you have not got it too
Kne