I have a strawberry tree and its dying do you have any information on diseases these trees get?

my strawberry tree is rotting. half is dead already. The trunk is split open I can see throug it and its got like a white powdery mildew, rotting look, Do you know whats going on? and can I save the half thats still growing? I water it twice a week for 1-2 hours. I only feed it once a year with fish almochion at least a gallon deluited, I dont know what else am I sappose to be giving it every nursery wants to sell me alot of stuff that very costly So I dont trust that there being honest with me, and so far nothings helping. The tree 6 years ago was so full you couldnt see the sky if you looked up from under it now all there is left are naked dead branches and maybe 6 that only have the ends with leaves but quiet a lot of new growth coming out as well only on a few braches, do I cut the dead branches off? and what about the trunk It looks like theres 3 trunks coming from the ground but it could be just one and then they divided at the surface, would you like for me to send a photo?