Avocado tree has stopped growing

I have a mexicola, winter mexican, and Lila that I put in whiskey barrels about 3 months ago they started off growing very well but here in the last 30 days they have stopped growing. I noticed the bark has this black powder look on them is this normal for young avocados? I really didn’t think the sun was doing any damage but it has been in the low 90s could this be sunburn? We’ve had a ton of rain as well but I did put potting soil in the whiskey barrels so they should be draining good.

The splotchiness looks normal to me, it’s possibly fungal but doesn’t seem to cause illness. Here’s one of mine:

Avocados go through cycles of dormancy and then flushes, so yours are probably in a dormancy phase. Water deeply with a liquid N fertilizer, and that might convince them to flush again. Sunburn looks more like this (first one is Winter Mexican, second is Poncho, they both got burned this spring when I moved them out from grow lights to full sun too quickly):

Edit:
Decided to consult Integrated Pest Management for Avocados and I think this is probably the culprit for the dark splotches:

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