Did anything out of the ordinary happen? Was there a hard frost in your area this winter? Did you use a lot of weed killer on the lawn or did someone spill pool chemicals?

Most of the problems people have with citrus dying are immature trees, container plants, etc. A mature 40' orange tree is pretty hard to kill. Overwatering, growing grass, lack of fertilizer and aggressive pruning will adversely affect your yield, but they shouldn't kill a mature tree, especially not one that size.

Regardless, I wouldn't do anything, including pruning, for a few months. If it was a frost, the tree should bounce back fairly quickly. If it was chemicals, it could still bounce back, but not as quickly or it may not come back at all.

Sounds like it was a nice tree :( Sorry to hear...

I would just echo wfspath...The only thing I would consider removing is is some *definitely* dead branches that you can reach if it is in large amounts, since with all this rain you may have some issues with fungi growing...And I also agree that is is pretty hard to overwater an in-ground tree in Cali, especially of that size, unless you were really going out of your way to do so. Why do you feel you were overwatering (rain notwithstanding)?

It sure sounds like it got "poisoned" all right...

You may want to think about removing any remaining fruit, so the tree can put any energy into recovery. And you may want to hold off on additional fertilizer for a while, too.

Did anything happen to the main trunk--any bark disease that may have girdled the trunk (especially if there were watering issues or lots of grass/mulch right up against the trunk) Or mechanical trunk damage from those weed whackers or mower or whatnot?... You mentioned growing grass underneath the tree--it wasn't there originally?

Last thing--with all the defoliation that it has had, be sure to think about what you want to do about shielding the trunk and branches from sunburn. It may not be an issue with this drippy gray weather, but it will be soon. I think you can paint the trunk and main branches with a white latex paint/ water mix or something like that, you may want to look it up...

HTH.
Hope it can recover.

Our "gardener" told me it was overwatered after all the leaves fell off and i asked him if he knew what could have happened. Just regular lawn watering, about 7 min/3x a week. Maybe its not that?

Not sure about any injury to the trunk- could have been hit by gardners lawnmower or weedwacker--but nothing that looks that substantial to me.

There are vertical splits in the trunk very thin, but about 4 to 6 inches long. I have looked online and think it may be foot rot or collar rot - a fungus of some sort. Does anyone know about this?

That doesn't sound good.

Doesn't sound like overwatering with that small amount. Is the trunk getting wet? That may be contributing to this bark problem. I'd cut back any vegetation for a few feet from the trunk and keep the trunk dry. Beyond that I haven't the faintest.

I've read that one of the original parent Washington orange trees got some sort of main trunk fungal infection or something like that and it was rescued by some sort of root grafting technique...something like that....

Good luck with your tree.

That happened to three orange trees in my yard. I had an arborist come to my house and he said there was no saving them. The green leaves left are from residual energy in the trunk. As I recall, he said it was probably a combination of not enough water (orange trees like deep watering and then to dry out between) and old age. I had also just moved in, the people who lived in the house before me wanted to cut the trees down (too lazy to care for them and clean up fallen oranges) so I surmise they never watered them. Shortly after I moved in we had an El Nino winter (lots of rain) so perhaps it was shock - too extreme. I don't know, but I sure miss walking out to pick a few oranges to squeeze for fresh juice in the morning. Don't blame yourself for the lawn though, my neighborhood is filled with orange trees in peoples front and back yards surrounded by lawn and they seem to do just fine. My condolences.

Meaning all due respect, I doubt that it was age. One of the original parent Washington navel orange trees is still thriving and producing in Riverside, and certainly that tree is much older.

Now water is another matter, though I hear all the time of old trees in CA not getting any additional watering except for rain...and having lived in SoCal with all these yards with their old, tall, and beautiful orange trees on block after block and I am certain they are not *all* getting cared for and watered "properly" :) Yet they thrive...go figure.

Sorry to hear about your trees too, greenwitch.

i am in california zone 9.i have 8 citrus trees about 30 yrs old,one is about 9 yrs old.a couple of yrs ago the leaves started to turn yellow.to make a long story short i finally figured that every time i turned the lawn sprinklers on the leaves would turn yellow and new growth would stop,this year we've had so much rain that the sprinklers have not been used.
even the trees i thought were gone,are coming back with new growth.i guess too much water is detrimental.keep us posted and good luck.