Is this pink root rot? I pulled an old frond husk off the shaft of my king palm. It's chalky and pinkish white. Above that it's a blackish color. Will this spread to the other trunks and is this something I can stop?

Yes. Sure looks like it to me. I lost a king to pink rot years ago and that's exactly what it looked like. Pink and powdery. The one I lost was a bit further along than yours so I just decapitated the trunk right below the crown shaft and used it as a pedestal to mount a bromeliad on top. I chose to get creative with it and that way his memory lives on. 

Definitely pink rot. You can either decide to remove it now or you can try hitting it liquid copper fungicide and/or hydrogen peroxide to see if that takes out the fungus. But if you see it actually causing damage to the trunk, it’s best to remove it. Keep in mind it could spread to the other alma so you’ll want to use the same steps to spray the other palm to prevent it from spreading.

Well this is a few days after spraying hydrogen peroxide on the affected trunk. What do ya'll think? Is it going to pull through or too early to tell?

I think if it’s that skinny it’s best to remove it. If I does recover and it could it could fall over from its own weight as it gets larger. I’ve had it happen where it recovered but was unstable so I removed it.

59 minutes ago, James B said:

I think if it’s that skinny it’s best to remove it...

Yeah, I'd remove the affected trunk. Though I'd probably just start with a new healthy palm (and disinfect the pot if being reused). At that size King Palms are plentiful & cheap.

One other consideration though... If the plan is to keep a palm in its current pot long-term, a King is going to be grow MUCH too large for that space. I'm guessing this was just a temporary location? If not (and you would like a relatively small palm for this spot) there are much better choices. If you'd like to upload a photo showing the location you were planning to put the palm long-term we'd be happy to suggest alternatives 😎

* Not that I don't like King Palms... that pot just doesn't seem like an appropriate placement for one (let alone a triple).

Thanks for help. I may just start with a new healthy palm. I have this palm in the garage under grow lights just until spring. It's interesting that the other king palm I put in my yard has done much better than this one despite a little cold damage. Unfortunately my yard gets almost no shade in the summer and with the multiple +100 degree days so fingers crossed it will survive with plenty of water and proper fertilizer. 

Well I cut the affected trunk off. Good thing I did since it had rotted through the whole trunk.