Have you called or visited your local extension office? In a citrus state, you'll find them more than happy to help.

Dang. The first thing that comes to mind is some kind of Canker or crown rot(Phytophthora)?

That tree looks pretty old also. How old is it?

That will keep spreading and getting worse. If that was my tree I would have chopped it off at about 2 feet down on healthy wood and treated the open cut and area with copper. But I know how hard it is to cut a tree that you love.

Do a search on Phytophthora spp. on Citrus. Its no joke. It usually starts lower from root damage or rot.

Here is a link that might be useful: {{gwi:585988}}

If that is Phytophthora parasitica I think once it takes hold there is really nothing you can do. You can treat the soil with a systemic fungicide but I dont know of any systemic fungicides. If its too bad you cannot fix it and your tree will die.

If your tree is OLD it might just be its time. I have heard of trees putting out HUGE bumper crops the year or two before they die. I dont know though and I wish you well.

I would definitely take some samples to your extension office NOW.

kbeard, we should stress that anyone growing citrus in a state where citrus is an important crop has a responsibility to report difficult or very sick trees to your Extension office asap. Homeowner cooperation is essential in saving the citrus industry in Florida. It may not be something lethal and they can also help you with that.

Here is a link that might be useful: Let's call your Extension Office right away!