Grapefruit tree dying fast

Greetings fellow gardeners! Something appears to be killing a grapefruit tree on some land I own in Florida. At the end of some branches it looks like something is causing the bark to strip off. While I was taking pictures to show I noticed some huge red ants and smaller but longer gray looking ants crawling on the branches. Today I was out looking at it and some bark was gone off of one of the main trunk/branches of the tree. Also, 1 detail that may help you help me is that I removed a few palm trees that had been blocking some sunlight to the tree. The parts of the tree that had be getting the shade turned a yellow green but seem to have come back.

Thanks!

The ants are the issue. Underground are 2 things.
#1 are tree roots
#2 ants nest (s)
So what happens is that the ants take up house in the nice cool, dampish, shady area in the trees roots, while there becoming comphy and at home there pulling dirt away from the roots, those roots dry out dangling amongst the new ant nursery thats expanding all the time leaving more and more roots hanging out to dry. The roots are like veins they go to specific areas feeding that specific limb, if that root to that limb dies, so does the corresponding limb, the limb dies, the bark peels as a reaction to the root death.
Amdro kills most ants that scavenge, for ants like carpenters get a good systemic drench because carpenters also do wood damage. With the systemic they bite the tree and die, but keep in mind as well you don't want to eat the fruit till the following year.
Trim the dieback off it won't recover only encourage other nasties to take up house.
Hope this helps

Well, that's a good explanation and makes sense. Thank you for taking the time to explain the problem.
It's been raining it seems like forever. Is it okay to administer either of the products you mentioned with all of the rain?

Sorry I don't get here often.
Amdro needs to be put down in dryer conditions, thats a bait that they take back to the nest and everyone eats then dies.
The systemic you choose will determine what conditions that are needed for that application and product so read the label carefully. Nothing is an overnight cure.
But I personally would do both when it gets dryer. The Amdro will quickly kill the ones you see and the systemic will take care of the long term problem.
Again, Sorry for the wait in this responds

Thanks again for the instructions and information.