yea, when you transplant... it shocks the plant bigtime. Avo roots are very sensitive. Trim out any dead wood (black) back to a bud or leaf. Keep the soil moist but not water-logged. It may come back.

Thanks fireduck, as it is creeping super fast down the main trunk, am I better off just topping the tree down near the graft? I hate to do something drastic like that but if it is slowly going there I would rather prevent now than slow cuts all the way to the bottom. Thanks

I had something similar happen with one in-ground last week - very healthy, got about 1' of growth (to about 4' tall) over the summer, then the top turned black, I cut it down below the bottom of the black part, but it the creeping-death continued further down the trunk. I cut it about 8" below the visible-damage to where there was no internal or external visible damage - it's now about 1.5' tall, but the leaves look healthy and happy, and it's been a week and no sign of further death. I don't know what it is - root rot, or something else (I hope it's not root rot, I have 3 other healthy avocados planted nearby!), but fingers crossed it comes back.

I would save all the healthy growth...pruning just above a bud or branch. Once shocked...these things do not recover overnight. Sunburn can be a major problem during heatwaves or when the tree is young.

prune off the main branch right above the branch growing to the left

Done, however I suspect it will still continue to spread downwards. I will update in a few days. Thanks

I found when I pruned below the blackness, I could see internally that part of the xylem was dry/woody. I continued to cut down, inch by inch, until there was no dry xylem visible in the cut. Unfortunately, because my tree is outside and in-ground, and I live in blistering Phoenix, I painted the first foot of the trunk white to protect it from the sun, so I actually can't see if it's turning black now. The one branch remaining still has some healthy/happy looking leaves on it, so I'm just going to wait and see what happens.

This is an interesting observation. I doubt it is to do with sunburn. Even outside this tree was mostly shaded. On the other hand I don't know what or how root rot works. I will be curious if my cut keeps the rot from going downward. If it does, like you cwlucking I can only think to prune the tree all the way down near the graft in hopes I cut out all the bad. I have NEVER seen anything like this. :(

Mine also in deep mottled shade, definitely not sunburn.

check out this interesting thread I found on stem canker

http://www.daleysfruit.com.au/forum/sick-avocado-tree/

I chose to make massive cuts to ensure no rot was remaining. Not the cleanest cuts but any thoughts on how xylem looks?

seal that pruned wound

how should I seal it?