How worn is too worn for a rope

I have an arborist rope (True-Blue 12 strand) and am wondering when to call it in? They can hold a tremendous weight, but mine is starting to get a bit fuzzy around the edges.... no nicks from cutting or anything. How do you know when to get a new rope?

Kenton

Alright, it looks like this is one of those questions no one wants to get even close to, I understand that. Maybe a no-brainer, if it looks bad don't use it... So, Treeman if you could just put me out of my misery...and make this question disappear...I will just use my common sense. Thanks for your anwers (or lack of them).
Kenton:oooops

Beyond the visible defects Padgett's "On Rope" 1996 page 36 says inspect the rope with a 10x magnifying glass. If more than 50% of the fiber bundles (pics) are torn, then retire the rope.

If anyone has a close-up photo of a rope at retirement age, that would be good to see.

Regards,
JimK

I will retire a 16 strand rope if any strand is cut completely through, or if any three adjacent strands are cut 50% of the way through.

No sense taking chances.

love
nick

ps- no, I don't adhere to these rules 100%. just guidelines