Oncidium 'Dancing Lady' with selective root rot...
 

Hi, folks - this is my first post (have been lurking since I set up an account, sorting through what I can find here). Am hoping one or two of the many fine knowledgeable people here can help with my plant issue.

And I did search the site, but didn't see much about damage just on the top of the plant.

So: I brought home a dancing lady oncidium from a nearby research gardens in mid-Judy, well in bloom. It unfortunately came with its own set of aphids; so I clipped the spikes and successfully dealt with the bugs. Pretty soon afterwards, it sent out a growth and is now 5" into a new pseudobulb (yay!).

I checked the roots at that point and they looked white and healthy, though crowded a bit. It's in a 3" square plastic pot with just sphagnum moss (from what I can tell). Given the new growth, I decided to wait until it started sending out roots before repotting.

So we settled down to a once-weekly soak for 20 mins, with weak MSU fertilizer once a month. It sits on my dining room table near a west-facing window (and a view of the house next door, though there is afternoon sun). And it looked fine. (Even with the cat occasionally chewing a leaf tip or two. ;))

Except in the last week or two, the aerial roots have started looking brown and moldly. BUT - the roots in the pot still look fine. So I'm not sure of what to do about it. :(

Some thoughts:
1 - Cut the aerial roots off, spray with copper fungicide, return to original pot.
2 - Cut off the aerial roots, spray with copper fungicide, put into a round 4" ceramic orchid pot.
After reading a few things here:
3 - Pull off the rotting part of the roots but do not cut, spray with copper fungicide, leave in pot.
4 - Pull off the rotting part of the roots but do not cut, spray with copper fungicide, transplant.
5 - something else I didn't think of.

Help! Because this was a semi-birthday gift, it was doing okay before this, and I do think I can save it.

Will the loss of the aerial roots heavily impact the health of the plant?

First, Welcome!

Photos would help. While some say that one has to make 5 posts to upload photos, I have seen new members upload them just fine. Click on the Go Advanced buttonm then scroll down to Manage Attachments. That will pop up another window where you can select your photos, then click Upload.

If that doesn't work for you, using some of the free internet services work... others will have to jump in and help. But seeing what you see is needed to start in terms of giving advice.

Welcome to the Orchid Board!

Fungus attack is very rare in lower humidity homes. Many exposed epiphytic orchid roots die back when moved from a humid greenhouse to a home. I suspect that is what's happening.

I suggest not using fungicides unless you know which fungus you have, and you know it is susceptible to the fungicide you plan to use.

Once a week watering might not be enough. Medium for Oncidiums should not dry completely.

Welcome to the board.

My gut reaction is “do not cut anything, and do not treat the plant with anything, as that might be a reaction to your growing conditions, not a pathogen”.

Where do you live? What is the humidity level?

Now with pictures
 

Thanks for the quick responses!
If I did this right, here are the images.

1 - the orchid itself (the new pseudobulb is on the left);
2 - the potted roots from the side;
3 - the aerial roots with the mung on the top; and
4 - the old and potential new pots.

I'm in NJ, and so far I only have an iffy hygrometer for the small terrarium I put together for a dendrochilum parvulum (a tale for another time). Am still looking for a more reliable hygrometer.

Is the house generally humid? Not in NJ - and the weather recently started turning, so it's only going to get drier. We had the a/c on during the summer, so it hasn't been very humid at all.

No pix... If you used the Orchidboard interface and used the pop-up... did click "upload" after selecting your photos? You need to do that before you post.,

Should be there now. :)

Oh - and it sits on the stones in the saucer. So a little bit of added humidity.

Indeed... thanks! What a gorgeous bunch of roots! I see no problems at all. As far as your choice of new pot, I'd stick with plastic pots. With those ceramic pots, as the plant grows you'll likely end up with roots coming out of, and winding around the holes. Then, when you go to repot, you either have to break the pot or trash good roots. If you have to cut a plastic pot to get a plant out, no big deal. A shame to have to do that with a pretty one (that also costs more) Your choice, just thinking ahead. Choose your pot to allow about 2 years growth. I would choose a 5 inch x 5 inch plastic pot or something of that sort.

Pot so that the oldest pseudobulb (the leafless one) is against the side, to allow for maximum room. Small bark would be a good medium - these do like to stay on the damp side. AT this point, I would not trim anything. The next time you repot (in a couple of years) you can remove the old pseudobulb(s) which likely will have begun to shrivel. But even the leafless pseudobulb is so nice and plump, I'd leave it for now, this is still a young plant and can use the reserves that the leafless pseudobulb can supply.

I agree. It looks good. Oncidiums should never go completely dry. A ventilated pot is for other orchids.

Don't be meticulous about removing old medium. You don't want to damage roots.

Ditto on ES's advice being gentle on the roots... as far as old medium goes, I just rinse under the faucet, or with a hose - whatever may be broken down gets washed away, but leave whatever may be stuck to the roots - won't hurt anything after that "bath". Root preservation is the priority.