Any idea why the main trunk of this otherwise healthy Rhododendron is dead.

Tony PLEASE STAY SAFE, KEEP YOUR DISTANCE

Hi Tony, not sure whats caused the die back of that trunk, but the soil surface needs to be free of all weeds & i believe the one thats filling this pot is pearlwort & the roots will surround the pot & potentially deprive your tree of any nutrients.

other causes of dieback could be poor drainage = water logged soil so when was it last repotted?

if the soil is constantly wet this would soak up the trunk & potentially cause the trunk to rot?

the species guide on this web site is a very valuable source of information: -
http://bonsai4me.com/species_guide.html

if you forget your history, you will repeat your mistakes, RoyH

Thanks Roy,

Two years since I repotted had planned to repot once flowering has finished ,do you think I should do that before?

Am not very good at this but pleased with how some of my little trees are doing,probably they look rubbish to experts lol.

Tony PLEASE STAY SAFE, KEEP YOUR DISTANCE

Hi Tony, i have no experience with rhododendron / azalea bonsai so this care guide below will be of some help

https://www.bonsaiempire.com/tree-species/azalea

if you forget your history, you will repeat your mistakes, RoyH

Thank you Roy,
I am going to learn a little bit at a time. For many years at koi club meetings I switched off when we had bonsai talks really wish I hadn't.

Tony PLEASE STAY SAFE, KEEP YOUR DISTANCE