Dying Oncidiums? Yellowing, spotting, leaf drop, etc.

[captainbug]

See attached pictures. All are intergeneric oncidiums as far as I know.

I let them dry out between each watering (which is why the soil is dry now). Repotted maybe 2-3 months ago into a dirt-bark mix.

I thought at first that it was just some shock and older portions dying off, but now it is affecting new growth.

I've got some gnats, but aside from that no pests appear to be present.

The one that is completely gone it seems like (left corner of the diamond in pic of all 4) wilted over between last night and this morning, and what I'm holding in one pic is those wilted over leaves that fell out with this soggy rot (which makes no sense considering FULL dry out and no water in 2 weeks). Is this related to the fusarium that killed off my vanda?

All of my phals, as well as one additional oncidium, are doing perfectly fine. Same water, same conditions, same lighting.

[rbarata]

All of my phals, as well as one additional oncidium, are doing perfectly fine. Same water, same conditions, same lighting.

The same soil too?

[captainbug]

Originally Posted by rbarata

The same soil too?

The phals and other oncidium are in miracle gro orchid bark, some smaller phals still in store moss/foam stuff.

I want to say these are in miracle gro moisture control mixed with orchid bark.

[rbarata]

I think your medium is not adequate, at least that's what it seems from the photos.
What exectly is a dirt-bark mix?

[Orchid Whisperer]

I suspect the "dirt". I think Fusarium is unlikely.

Take the problem plants out of the soil, I suspect many plants will have few out no live roots, and many pseudobulbs going brown/soft at the base. Most of the orchids we grow are epiphytes (live in trees, have roots exposed to air) and won't tolerate roots in soil. The roots need exposure to air and die/ rot without it.

For those living plants, try repotting in orchid bark (look for Better Group brand at Lowe's). Add chopped long fiber sphagnum into the top inch or two of bark in the pot. For Oncidiums, the medium can stay slughtly damp beween watering.

[captainbug]

What do I do about pseudobulbs that look dead? Leave attached for now, or detach?

[Ray]

If they're still green, they're still contributing to the welfare of the colony.

[captainbug]

Do the bulbs ever plump up again? Since purchase many have been wrinkly and thin, while others are plump and thick.

[rbarata]

They may recover just a little bit but never like they were before. In the meantime others will grow new sodon't worry. Just take the plants out of that medium and pot it with a coarse mix of medium grade bark plus LECA (or anything equivalent).
Good luck

[captainbug]

Amazon is now 2 days late delivering the bark for these orchids... Would it be better to dump them out of pots entirely and let the roots remain exposed to air while I continue to wait for the bark?