Help! Large Black Patches on 2 BLC ShingFong ‘Tian Mu’s

[realoldbeachbum]

I purchased 2 of these orchids 1.5 years ago from Triton Orchids (thru Etsy). They thrived in my environment until 4 days ago. I was on travel for 4 days and returned to large black patches on over half of the growths. The patches are mostly on the tops of leaves, but appear to be bleeding through to the underside on some leaves. None have reached the top of pbulbs. Pbulbs are green & healthy, and 2 new growths have no patches.

From photos on St. Augustine’s website, it appears to be sunburn, but they have been sitting under the same grow lights for the past 1.5 years with no increase in light. The other 4 Catts on the same shelf have no such patches.

What do you think this is? How would you treat them if they were your plants. (I have isolated them.)

All advice is appreciated!

[Dimples]

What were the indoor temperatures in the house while you were gone? If you set the AC to a higher “away” setting, the leaves may have gotten too hot, even though the light level didn’t change? Just spitballing.

[rbarata]

To discart possible sunburn one must treat the scenario as a crime scene.
Before panicking, don't move the plants and check if the spots have something in common, for ex, same side (faced to the light source), mostly on top etc. See if the spoted areas are directed to the light source, etc.
If not, probably, it's not a sunburn issue.
Anyway, more details are needed, are the spots growing? Do they feel wet or dry? Only older or younger leaves (or both)?

[estación seca]

That's sunburn. The plant is dried out - lots of wrinkles. Such plants close their stomata and don't evaporate as much water to cool themselves.

[realoldbeachbum]

Thanks ES, rbarata & Dimples. I believe Dimples hit the nail on the head. While we were away a microburst knocked out electricity in our area for 18 hours (destroyed neighbor's house). With the AC off for 18 hours and the next day's sun beaming through the windows, the temp in the grow room was probably near 100 degrees. Also, the fan wasn't working -- so no air circulation.

Now that I think about it -- the grow lights were off as well -- so it wasn't a "light" issue, but a temp issue. The spots are not growing and are mostly on tops of leaves.

It is interesting that it only affected the 2 ShingFongs and not the other 150 or so orchids in the same area! Oh, these orchids -- such a mystery sometimes.

Should I chop off the damaged part? (That will make for some UGLY plants for the next 10 years!!!!)

Thanks

[rbarata]

Different species have different tolerances to the vast array of environmental parameters. This also result in different symptoms when the parameters go over the tolerance limits.
I wouldn't cut the affected parts but that's just my practice. If you leave them it won't hurt the plants.

[estación seca]

I leave sunburn alone. It dries to a papery consistency. If you cut you will remove good leaf tissue as well.

[Dimples]

Once it dries down fully, if the entire end is dead, I’ll do some trimming. I try to curve the cut end to help it look more natural vs a straight line. Partial burns stay until the leaf drops.

I’m glad it wasn’t an issue with your setup. Are your neighbors ok?

[realoldbeachbum]

Thanks Dimples. The damaged areas are not increasing (I circled the edges to be sure), and neighbors have NOT exhibited any spots. (Keeping my fingers crossed!)