Moni

Heh, heh. At the risk of really throwing a nail into the works here, might I suggest the pine bark adelgid? That would also explain the black sooty stuff that was observed at the beginning of this poor pine's problems. An adelgid is of the aphid family.They can be much smaller but they exude honeydew just like normal aphids. The honeydew gets moldy and looks like black sooty stuff which can be washed off. They are a problem on pines out here in the great northwest. Don't know if they are a problem there. You may need a 10x lens to spot them.
If it is a fungal root problem, Subdue is the way to go. But I would look at the roots first. In root rot it is the nice feeder roots that are the first to disappear. Not a good thing for us.
Moni