Avocadoes don't get fireblight.
It's not normal for an evergreen tree to lose all its leaves.
Avocadoes do get root rot.

The only way to know if you are watering too much or too little is to stick a trowel in the soil & look/feel.

At this early stage after planting, the greatest need for moisture is in the region of the original rootball.

So this tree has root rot, any suggestions on hot to cure the problem. Should I dig it up and cut bad roots or hold off on watering, this is my fourth avo tree and they all have died this way. I have two plum, two cherries, three peaches, two lychee, two pear and all are doing well. I've killed Avos and the mangos.

So this tree has root rot, any suggestions on hot to cure the problem. Should I dig it up and cut bad roots or hold off on watering, this is my fourth avo tree and they all have died this way. I have two plum, two cherries, three peaches, two lychee, two pear and all are doing well. I've killed Avos and the mangos.

When the previous avocados died, did you dig them up and look at the roots? If they were black and shortened, it's likely root rot.

If the tree has root rot, there's no available treatment.

If root rot is the underlying problem, you must use only root rot resistant plants in that area or nearby, possibly your entire yard.