That is not good. I would quickly remove it and cut off the section on the left that doesn't seem to be effected. I've heard of them "rotting" and that looks like what's going on here. It could be getting stung by something if there's anything close but I don't think there a whole lot to be done at this point. If it were mine, I would remove the piece, frag off the part that's still healthy an dip both of them in a logul's solution.