Pictures are always helpful. Your growing location and conditions will also be of assistance.

Harry

You can take a look at the leaves at this url:

Forum di agraria - Mango

I'm growing my mango in Venice, Italy, (45ðN 12ðE). It is a coast city with mediterranean climate. I put the seed in a clay pot (gravel bottom to help drainage plus general fruit plants soil). It is now placed in full sun-light in my roof terrace. I water it almost every day.

I haven't seen that particular leaf spot pattern before so I can only provide you with a general answer. The vast majority of mango disease, at least in the tropics, is fungal. There are some viral diseases as well, but they really are not well treated. So if this is viral, the plant will either out grow it on its own, or go into decline or eventually die. Not much you can do. If fungal, a good fungicide will definitely correct the problem. Since your tree is not fruiting, it is most effective to use a broad spectrum systemic fungicide. You could spray with a topical spray, but that would require multiple applications and will probably have slower results. Sorry for being so general. I hope this helps.

Harry

For mangos in pots, I had problems like that when I water a lot. The leaves will eventually fall off. Now I keep them mostly dry, and the trees do better. I only water when I can tell the bottom of the pot is dry. Good luck.

-Tom

Looks like some type of fungus. I would go with a copper fungicide, and drench liberally.