Yellow Shrivelling Pseudobulbs on Oncidium

[Mercurius]

I inherited this Oncidium from work (nobody else was capable of caring for it) and it's been having some issues. Some of the older bulbs are yellowing and getting all shrively and losing their leaves. I thought at first that it was just the older bulbs dying off, but the one at the far left of the pic had a new bulb starting that just also turned yellow. I typically soak it weekly with dilute fertiliser unless it seems too wet/dry, then I adjust accordingly. It used to sit on the kitchen counter with my phals and get the evening sun, but a few weeks ago I moved it to an east window with some other phals.

[estación seca]

Ave, Mercurius!

It could be dead roots, not enough water or bugs hiding at the bases of the pseudobulbs. I would unpot the plant (unless you've done that recently), remove all the old medium, and examine closely. I'm going to guess you haven't been watering enough.

Oncidium roots are very thin compared to most other genera. When healthy they should be white, green or light brown when dry; they should not pull off easily; they should never be slippery, mushy nor black. They should not fall apart easily. The commonest cause of dead Oncidium roots is overwatering, though I think that's pretty hard to do in decent bark.

Plants with pseudobulbs dying of dehydration normally have pleated leaves. I don't see those on your plant, but I don't see the whole plant.

If it's bugs, you will see them. Treat with an insecticide.

If the roots are rotten, cut off everything that is rotten. This will probably include the yellow pseudobulbs. Sterilize your blade between cuts with 10% bleach solution for 3 minutes or heating. Stop cutting when you are into fully green tissue.

If the whole rhizome is infected, the plant is dead.

More likely, some of it will be alive. Let it dry for a few hours and repot into fresh medium. People use all kinds of media successfully for Oncidiums. They need a lot more water than other kinds of orchids, but they also need air at the roots, in common with other kinds of orchids.

Water when almost dry. You can learn to use wooden cooking skewers to check dryness

here.

Good luck, and please show us photos when it blooms for you.

[Mercurius]

Here's a picture of the rest of the plant. It doesn't really seem like dehydration because the rest of the plant is still pretty plump and green. The yellowed bulbs are still fairly firm, too. I'll definitely re-pot it and check for bugs, though.

[estación seca]

The rest of the plant looks fine. Is it possible that reflects different care than the plant is receiving now?

Watering an Oncidium once a week might be reasonable under some conditions. Many people need to water them more often, especially when pushing new growths, and when in bark.

[Mercurius]

The only change in care has been moving it from the kitchen counter to the east window. I was afraid maybe it wasn't getting enough sunlight where it was on the counter. I've had it a couple months now and it was doing ok aside from some older bulbs dropping their leaves. I assumed it was part of the normal cycle as it has quite a few new growths on it, but decided to move it in case the amount of light was the issue instead.

[bil]

Originally Posted by estación seca

The commonest cause of dead Oncidium roots is overwatering, though I think that's pretty hard to do in decent bark..

PREACH IT SISTAH!

To me, that is such a signal truth. I would go one further and say that IMO, if the medium is properly open, and is not degraded, it is pretty hard to overwater.

I like to melt a hole near the bottom of the pot and shove a bamboo skewer in horizontally. That gives an absolute indication as to water retention, and is wise, as medium degredation can creep up on you.

I tend to think that a yellowing, soft p-bulb is going home and is best removed.
As Estacion Seca says, if you haven't repotted it, now would be a good time. With mine, where I know that it doesn't need repotting, and one of my p-bulbs goes like that I just cut it all out with good scissors, and then I dust the cut surfaces with Mancozeb powder which is my go to for fungus prevention and treatment.

[mBluebear]

Hi,
My Oncidium had that problem before. Turned out that there're many tiny snails hid behind the roots.
I repotted the orchid, removed al the snails in the roots, and put snail pellets on the top of the medium. Not sure if there're any snails left.

You should repot it and check for any pets hide in the roots.
Good luck

[Mercurius]

The larger bulbs aren't really soft, though, which seems kinda weird. What it looks like is when a plant gets frostbitten and turns that off yellowy colour. It hasn't been anywhere cold or even chilly, so I know that's not it. Would powdered cinnamon be appropriate for on the cut surfaces after removing the yellow bulbs or would that dry them out too much?