I know Keith that my potted Mangos would look ok,but when I tried to put saucers under them in summer? The small amount of standing water that they were supposed to wick up?...caused the leafs to do like yours. It only took a couple of days.

So,salty mineraly water or soggy root tips both are hated by the trees.

Thanks for the info, Stanofh

Sorry, probably best to move it for the long term health of the tree. You can look into building it in a raised bed or something also. Mangoes have decent sized roots when mature so as far away from the canal as you can manage is better for it in the long run. How cold does it get where you live? You might be able to put a more salt-tolerant fruit tree in its place.

Just wondering if you ever positively identified the problem? Did you have any luck getting rid of the brown leaves?