Without pics it's tough but my hunch is the tree might be getting hammered by bugs and borers and the flies are attracted to the sap or laying eggs, even lay eggs into host bugs.
First off, you need to decompact around the tree, get some liquid organic material happening, maybe some mulch.
I'm not sure how big the tree is etc but you need to treat them bugs, over here I'd either spray, inject or drench with Confidor, rogor or carbyrl.
Funny, just today I went and had a look at a bunch of citrus trees doing similar. |