Wils. pbulb beginning to rot?
 

About a week and a half ago, I purchased several bare root seedlings at my local orchid show. One was a Wils. Red Stars 'Rooster' that had three pbulbs. The roots had been wrapped in damp spagnum moss at the show and when I got it home, I potted it in some small piece bark mixture. Now the Wils. looks like it's starting to rot at the base of two of the bulbs along with some of the leaves. Is there anything I can do? Any ideas of what I did wrong? I don't see this happening with any of the other seedlings I purchased. Thank you!

Unfortunately, once pseudobulbs begin to rot, there is nothing you can do to cure them so you will need to remove them before they infect the last pseudobulb. The remaining pseudobulb will probably put out a new growth eventually (the Oncidium family tends to be pretty good concerning that) so the orchid should recover. If you have a systemic preventative on hand to prevent infection in the last pseudobulb, it might be a good idea to use it.

I'm guessing it's best to remove the whole bulbs? I know you can sometime cut away the rot, but i'm guessing that's not a good idea in this case due to the location of the rot.

If you want, you can try to cut away the rot and see if there is anything worthwhile left. As long as the infection doesn't spread into the healthy pseudobulb....

If you can save some of the root area and an eye on the new bulbs, they may not fully grow but they would be able to put out new growth.

As for why this happened, I really don't know, but when I was googling the name of your orchid to see what it was like, it seems like someone else, a few years ago, had the same thing happen with the orchid, too. Perhaps it is just more susceptible? No idea.

Yours might be different but I found, when I had an Onc. that had bulb rot, it was best to cut well into green healthy material. I tried removing only the rotted bulb and a bit of green tissue several times and each time the rot continued to move to the next growth until I had very few left. It wasn't until I took the bad bulb plus the good one next to it that I finally stopped it. I guess the bacteria is there in advance and just not showing visible sign. I hope you can save it.

Well, when I tried to cut just the rot away, I found both bulbs were rotten in the centers so I removed both of them, applied a little hydrogen peroxide and dabbed them with cinnamon. I'm only concerned that I didn't cut deep enough into the rhizome to get rid of all the rot, but I didn't want to be over zealous. This is my first time treat pbulb rot. I took some pictures as I went, just so others could see what was happening.

First two pics are the bad pbulbs. The next two pics are where I started to cut into the pbulb. The fifth picture is the inside of one pbulb I removed. The last two pics are post removal after I applied the hydrogen peroxide.

Hopefully I can save the plant, but if not, at least it's been a learning experience.

I was afraid that was what you would find. :(
If the old pseudobulb stays healthy, it should put out new growth. Just keep it warm, give it good light/air movement and water from below (don't get any part of the pseudobulb or leaves wet). It wouldn't hurt to keep it dry for a few days. I usually like to dip a cotton ball in isopropyl alcohol and clean off the pseudobulb and leaves to disinfect the plant...just in case.
Good luck!

I don't think that you did anything wrong, the plant probably had this problem before you got it. (that sphagnum root-wrap unfortunately can hide all sorts of ills) Good luck with your rescue efforts!