Looks like they've just dried out, lack of water.

My guess is its either overwatering or underwatering. Overwatering has similar symptoms than the opposite underwatering. Stick in your finger, and if its moist down beneath the top soil, I'll leave watering for now.

My mango dropped its top leaves and the lower begun drooping severely. Then I recognized that the soil in the bottom was pretty moist, almost dripping wet and top soil was crusty dry. And it was one and a half weeks after last watering. Its in room temperature (70F) in a 3liter(approximately 1 gallon) pot with no draining holes. And I've been watering sparely.

Its seems you have a plastic bag over the "growsack"(whatever its called, sorry my english)? And if the floor is cool, its pretty easy to overwater.

And does it have any draining holes? If not, make some and quickly.

Check the weight of the bag, stick in your finger: if its heavy and moist, dont water.

If its light in weight and soil feels dry: water it.

Nothing else I can offer to you. (And you probably already knew these..)

They are all in grown bags or my own air pots and I had my watering schedule according to the dryness of the soil. I showed pics to my local garden center expert and he thinks it's a fungal attack.

Jontte did your leaves become brown or black before they fell or were they still green but wilted and fell off?

New growth stunted, were curled and ended up brownish and papery from the tips(some went halfways dry) before I clipped them off. Half of the old leaves too ended up being brown and papery. I did prune it simultaneously, taking a change it would have died. But its recovering slowly but steadily. Pushing out new shoots.

The wilting and dis-coloring started from the top making its way down(we do have really low hudminity indoors during wintertime, it surely sped up the process). It took two days to get that bad. I did change the soil and washed out the roots. None of them was rotten, but would've been really soon.

I have no idea what fungus attack looks like. But if it is fungus, you could probably use some baking soda mixed with water as a home-made remedy? I dont know the recipe for that, but google sure has the answer. Thats the only thing I can come up with of it is fungus.

Are the leaves still soft or are they crumbly? If soft, you might have a chance saving them. Otherwise they are 90% dead and useless for the plant.

time to cut it right back

If it was warmer I would have cut them already. I'm not sure if they will survive pruning in the middle of winter. Matt have you pruned in winter before?

I am no expert with mangos. I had a leaf do that same thing last week. It was severly dry. It's a good idea to let it dry a little between watering it keeps the roots looking for moisture but only for 2 days max then I replenish. This time I let it go too long. I haven't pruned mangos but I've pruned other plants this winter and they are all doing just fine.

Where are you located?

NY zone 7

I've cut back before but always close to the end of summer after I get fruits. Last season I lost one after pruning back almost 2/3 which may have been a bit much.

Ohh they're giving you fruit already!! yes never more then 1/3 at any time.

Mangos are usually tip pruned during harvest but the heavier pruning is only done after harvest. They can be pruned back severely (and I also mean down to a stump) and they come back without a problem. If you have rain or high humidity you'd need to paint over the cuts to prevent fungus getting in as that will be what could kill the tree.

That tree looked frozen from cold. I have pruned this winter with success

If it comes back I will update with pics.

i am thinking you had a watering schedule, and in winter, they needed less water, hence they stayed too moist/damp, and yeah that can lead to fungal attacks.

its really hard to diagnose a dead tree

Yuk yuk... does your local garden guy grow mangos up yonder??

Unless they do, for tropicals I would say his / her advice is not worth getting.

Mango down here do surprisingly well in long spells of dry and wet. With good drainage and an attentive eye water should not be the issue. Humidity is another thing. Most heated homes are very dry in the winter, maybe that is your culprit. Folks who try growing mango in hot dry climes do poorly. Tropicals like humidity, but then too much like having lawn sprinklers on them in evening leads to fungal issues.

Humid and cold like you said may be the problem with those, HOW cold?

BTW, by long spell of dry, I "MEANT" an attentive eye to correct the dry condition with irrigation, I hope Y'all "read tween' the lines" on that. Also our water table is not very deep, mature mango seem to do well on their own with little watering, our potted specimens need a watchful eye.

The "Finger in the soil" method will tell you if the tree could use some watering.

so they survived?

I will guess too wet in a soil too heavy. Once the roots go,there is no saving a plant.

A second guess it some phytophera...but thats the result of too wet,etc.

Mangoes have a very fine root system. They need a lot of air down there. in the ground they get air in even a clay soil...but in a pot? The peat or humus just sours.

Have you used neem on them before? They look burned

Yes I neemed them when I thought it was a fungal attack. In a few weeks I hope to put them in the ground and see if some will recover.