How long has it been in the ground. Where do you live?

I am in Houston, it is in the ground for more than three years.

Although (my) mandarins are persnickety, they should be setting well after three years in the ground. Could it have dried out since your last rain? Have you fed it? If so, how often, with what and where?.

I had a similar looking mandarin years ago, but in my case, I gave it food, but not enough water and therefore burned the roots rather badly. My solution was to increase the irrigation 2x and water more frequently in the heat. I also gave it a weekly dose of liquid (high N) fertilizer + vinegar solution.

Another possibility is latent freeze damage,.,, did you have a freeze in your area? I have had trees (for example my 88-2) drop nearly all of their leaves and wilt. But that was due to latent branch dieback from freezing temperatures.

I didn't feed it, the weather was warm, and the upper soil didn't dry, it has a lot of flowers in the spring. It's so weird, I don't know what's wrong with it.

No feeding? Citrus is a hungry variety!

Well, perhaps the leaves are being sacrificed to produce the fruit I see hanging on it. Its also possible the leaves are 2 years old and in the normal process of being replaced. If it were my tree, i'd give it a weekly feed of a high N liquid food solution (I use Master Nursery Liquid Gold) along with a tablespoon of vinegar per gallon mixed in (because my water is 9.2+ pH). I'd also begin adding a spread of 1/2 cup of Ammonium Sulfate every week in between. Its spring flush time and now is not the time to skimp on food!

Molewacker, thank you so much! I will fee it, hope it can survive.

Molewacker: for me it sounds a bit odd that a tree sacrifices the leaves to grow fruit? I've always thought that the leaves are the powerplant of the tree, and if it needs to get rid of something, it would be the fruits in first hand. I'd like to hear(read) the theory behind this :)

I believe the problem is root rot due to the roots being water logged. Is the soil wet or damp about 8 inches down?

Do NOT give it fertilizer. That may kill the tree.

I too have never heard of trees dropping leaves to grow fruit.

Winter Sweet, Best to you as you try to help your mandarin. I'll second the comment that you may have some lingering damage from the freeze we had. We really only had three days of winter here this year but it got down into the 20s. I just recently found the bark had split on one of my trees due to the freeze. Hoping for the best but if you do have to replant, I highly recommend doing a raised bed (8-12" above your native clay) and back filling the bed with something that drains better. I am also growing citrus in clay here in the Beaumont area but I see a world of difference in the one tree I have in a raised bed.

Unless this tree is sitting in a pool of water it is NOT overwatered. John9a - 3 days of 20 would likely cause what we see. I also concur with JohnM - stressed trees will bloom and "fruit" rather than make leaves! ...Remove that fruit to give it a better chance. It is stressed and needs a quickly available feed (forget the organics) - right now.

BTW: as we know, citrus leaves will look similar overwatered and under watered. But, the clue here is the healthy looking leaves near the base of the tree. Underfed citrus is especially susceptible to freeze damage (possibly because the bark has not fattened up?)

I nearly lost 1/4 of my in-ground trees due to worries about overwatering... because so many potted citrus growers have such issues and I was reading their stories here. But, shoveling down to investigate, ALL were dried out excessively. Doubling and tripling the water fixed the problem. I should note that there was one exception, and that issue was caused by a irrigation leak 3" from the trunk. That tree was pulled and potted; and has produced some nice tasting Oroblancos the past two seasons : - )

Good luck and keep us updated... we love pictures here on this forum!!

Just want to make a correction to what I said earlier. Citrus will drop a relatively small number of leaves when putting out blossoms.

I think my tree is dead :( just one day, it looks like this

I checked the tree carefully and I think I found the problem, look at the trunk, there is a circle damage on it

Thanks everyone for helping !

Feeling for you Winter Sweet. Looks like it's a beautiful tree and keeping fingers crossed that it's just bigtime stressed and will be sprouting new leaves in a couple months. Hoping there is some solution to the damage on the poor thing. Wishing you and your pretty tree well.

John: thank you for the answer:) you learn something every day..

Ah, so the damage is why the leaves look awful in the upper part of your tree but look healthy down low. Almost looks like there may have been a wire or other tag securement there from the nursery. The leaves down low are above the graft so they should grow up and make you a nice replacement pretty quickly since you already have a root system for a bigger tree.

John, you are right, there is a wire there before, I think it already damage the tree before I took it off, you think I can keep it?

Aha - indeed! it should recover to a producing tree... IF the new growth is from above the graft. I cannot the graft in the picture./. unless the graft is where the damage is? If the bottom leaves are same as the top ones that are dying / died then you are in luck. Sometimes the scion will sprout a new shoot just at the graft line and it will all work out. Investigate closely and if you decide to keep it, patience will / should reward you.

Do you know by chance where the tree came from (source nursery) and the rootstock?

I think the bottom leaves looks different :( I bought it from Houston Garden center, here is the tag

I think I'd better buy a new one, which type of mandarin is sweet and juicy? Thanks