My first thought was that this was caused by a phytophthora canker, very common in commercial avocado. But a bit of reading indicates that there are numerous possibilities (click here) for a crystalline deposit.

Your local UC Extension office would be a good place to get advice. We really, really can't be of too much help without seeing the whole tree or knowing the kind of conditions in which your tree has been growing.

Thank you for finding that for me. Since the tree seems really healthy I guess it would be from an injury to the bark. Nature is always so complicated.

I wiped it off, ...... Sure enough a week later the crystal white stuff came back. I am assuming it is some
type of injury to the tree and it's trying to heal itself? But then why
doesn't it.

==>> you arent thinking in tree time.. as to how long it takes a tree to 'heal ' .... think more in terms of years ...

we dont do avocado in MI ... so i cant be more specific ... ken

Do you think if I plugged the little hole where it's oozing from with some epoxy it would help?

No. Trees generally have reasonably good mechanisms for healing themselves. They never heard of epoxy!

I wonder if it has some kind of borer in it.

John....no, you cannot glue or plug the hole. Your tree can't be fixed or cured from an infection like that, either by you or by a physiological mechanism. (Sara's comment was highly misleading).

Not sure why it was misleading - this could well be from injury. If not from injury, the first three pathogens are problematic after low rainfall years and CA had one of the wettest winters on record, so sound unlikely. The fourth pathogen, a species of Phytophthera, causes cankers that appear at approx 18" off the ground. Unless I'm reading this wrong, this wound is much higher up.

Sara

yeah hard to know for sure but given the weather, location and the fact that it is solitary, the working hypothesis is injury. But remember, keep testing that hypothesis! Wish avocado would fruit for me. We're just not warm enough for them to set fruit easily in most parts of the Bay Area.

It seems to not always fruit well. Last year, there were many. This year, not as many and all that rain over the winter you would think there would be more. But they are incredible, so much better than anything you buy in the store.

Many fruit trees (and maybe other plants, too) are alternate bearers - they alternate between a big crop one year and a smaller one the next, then repeat the cycle. Japanese persimmons and olives are two that I have experience with. Sometimes you get two bang-up years in a row; I had about 250-300 fruit on my Fuyu persimmon last year and this year looks about the same. Avocado may follow the same pattern. They look yummy!

I am not happy, somebody had posted what the issue is on a previous post I made on this. Here is the link, any additional comments. :-( !

https://www.houzz.com/discussions/white-crystal-like-substance-coming-out-of-trunk-dsvw-vd~4813615

More information and who to contact here (also on other thread).