Mango fungus help

[Julie]

This black mold/fungus started on my Glenn tree and now is on my Pickering as well. It starts as one spot and spreads. Is this damaging to the tree? What is this? Do I need to remove these trees to prevent it from spreading to my other mangoes?
Pickering:

[Julie]

Glenn

[Julie]

Glenn

[roblack]

Looks similar to what's on our mature Glenn tree. Sent pics to Alex a couple of years ago, and he said he has seen the same on some of their trees, and does not appear to be a problem.

[Jose Spain]

Seems like a lichen to me.

[Julie]

Looks similar to what's on our mature Glenn tree. Sent pics to Alex a couple of years ago, and he said he has seen the same on some of their trees, and does not appear to be a problem.

Thank you rob for replying.  Has yours been spreading on your Glenn tree and to other trees?  At first it was only on my Glenn tree for several years (but spread throughout the tree), now it's on my pickering tree as well.

[CarolinaZone]

Has any body here tried systemic fungicides? It worked for my quince trees.

[Julie]

Has any body here tried systemic fungicides? It worked for my quince trees.

No, I'm trying to keep 100% organic and something systemic would definitely get into the fruit.  Does anyone else have any insight into this?