Pitting on Phal leaves

[camille1585]

A lot of my Phals have strange pitting on their leaves. It started about 2-3 years ago, right around the time where my Phals were subjected to a lot of neglect, so I'm guessing some opportunitic fungus got a foothold in my collection. The problem partially went away with good, regular care of the orchids, but it's still there, lurking, and afflicting a lot of the new leaves, especially in the winter.

My first guess was spider mites, but wiping with a cotton doesn't show tell-tale residues on the cotton. My second guess was possibly virus since I also had a mealie bug problem during the period of neglect. But even new Phals are getting it, that are on a different shelf (in the same room), and never had any contact with the infected Phals. Everyone is watered separately, and I sterilize tools/pots when repotting. I never get water on the leaves, and it's never cooler than 17-18C (roughly 60-65F), so I don't think it's mesophyll cell collapse either. And no other genera are afflicted, it's only the Phals! My Phal. equestris and equestris primaries seem less affected though.

After a few years of this I think I see a pattern: it's worse in the winter, and in spring/summer I hardly see any new spread.

The obvious solution is to stop buying Phals, but those are my favorites and do exceptionally well for me.

Any ideas on what this may be and what can be done about it?

[wintergirl]

Wondering if your humidity is too low.

[silken]

I hate to say but it looks like what I learned was poty virus. It looks a lot like mesophyll cell collapse: https://www.google.com/search?q=meso...HeXtBZoQsAQILg. And it might be but poty virus looks much the same and from my own experience affected every Phal in close proximity. I don't think there is a cure. The new leaves grow out nice and healthy looking and you figure the plant is getting better, but it just takes time to move into the new leaves. Mine had great roots and bloomed beautifully despite this. But it spreads like wild fire and in the end I tossed every single Phal I owned pots and all, and tried to thoroughly disinfect the whole area.
A year or two later I tried a couple more Phals in the area and they got it. Doesn't seem to affect any other orchids I have unless it is the cause of spots on some of my Onc. which seems quite normal and many other people have. Several years later, I have ventured to have about 5 Phals in my living room, not the greenhouse where the sick ones originated. I am sure it all started with a grocery store Phal I won in our society raffle. Soon after I brought it home it showed symptoms and people said spider mite and mesophyll cell collapse. No spider mite and I had not given it cause to have the cell collapse. From there on all Phals contracted it. I tried Physan and certain anti fungal/bacterial treatments all to no avail.
Jerry from OrchidWeb had an article on it a few years back and said it is believed to originate in Taiwan and the plants all look healthy under optimal greenhouse conditions, but once put thru the stress of shipping and being in box stores etc. they succumb to it and begin to show the symptoms. He knew of a commercial seller who lost an entire greenhouse full of Phals to it.
I hope its not what you have but I know several of my orchid friends have had the same problem and seen Orchid Board members with similar symptoms. Good luck.

[Whimgrinder]

That is absolutely mesophyll collapse. The question is, WHY is it happening. My first guess is cold water on leaves, but you don't do that, so.... I think Silken's theory is the most likely scenario.
Whatever the cause, I would not hesitate to remove and destroy the plant, and any neighbors that show similar symptoms.

[camille1585]

Originally Posted by wintergirl

Wondering if your humidity is too low.

Humidity is in the 50-70% range, so pretty good for orchids.

[Leafmite]

I am not sure what it is causing the issue but this is the website that I think has the best pictures for orchid viruses:
http://www.orchidsocietynsw.com.au/D...id_Viruses.pdf

Agdia will test for the potyvirus and I am sure that there are places in the Netherlands that will also do it (as they have a large agricultural industry).
https://www.agdia.com/testing-services/Orchid.cfm

It may not be a virus, though. Is your place (or window) a little cooler than the idea temperatures for Phals? I had a new Phal violacea and I thought it would be okay with the cooler night temperatures but the leaves developed pitting. I put it in my mini greenhouse that sits on a heating pad and there has been no further damage on the leaves (and it has not spread to the other Phals).

I also wonder if there are tiny mites that are impossible to see, even with a magnifying glass. Last year, I saw quite a bit of damage on many of my orchids that really looked like spidermite damage. I even lost some of my orchids. I didn't find the mites, though. When I put them outside, I noticed predator mites and lady bugs were soon all over my orchids...they must have found something. This winter, I haven't had any issues. The new leaves have been good. I have not changed my conditions so if there was a virus, logic tells me that I should still be seeing the same issues.

It could also be a nutritional deficiency. I lost my link to a very good site that shows the various types of damage caused by too much or two little of the various nutrients and, in some cases, the symptoms look like pictures of seen of probable virus issues. If this was the problem, I have no idea why the problems would be worse in the winter, though.

These are just a few things to consider. Not everything is caused by a virus. Having a lab test them for you would be the only way to really know. If you are fond of the orchids, you shouldn't toss them out until you know the cause of the leaf damage. The fact that the new orchids have no discernible transmission vector for a virus is rather curious.

[camille1585]

(Poty)virus is a possibility, but how on earth is it spreading?? As far as I know there are no airborne plant viruses. I have been extremely careful with the 'new' Phals and infected Phals, and they've not any direct contact, or had tools used in common on both groups.

But for the mesophyll cell collapse, seeing as it seems to spread more in the winter, it could be possible that the cooler air near the windows is part of the problem. But why should the problem appear now, when I grew some of the same orchids behind a window for 7-8 years before the problems started. And the past 2 winters have been extremely mild, it hardly went below freezing so it wasn't that cold behind the window. I'll stick a thermometer there tonight.

One thing that may hint that it's of fungal/bacterial origin is one Phal I tested something on. That one had all it's older leaves badly affected, so I pulled them all off last spring, leaving only 2 leaves and then isolating the plant. It grew a new leaf over the summer, and so far the entire plant is still symptomless. So that would indicate a non-systemic pathogen, pretty much excluding virus.

In any case, I'm not tossing anything until I have some sort of definitive answer to the virus question. If it was just a few plants, fine, I'd toss. But in this case it's a bit hard to stomach tossing close to 70% of my collection on a supposition. It's a lot of money and years of effort that can't be discarded lightly.

I'll take a few plants to work with me this week and check them out under a binocular microscope to check for mites. (I work in plant science). Next step is getting plants tested for virus, but is there a test (home test or send off for ELISA) for the taiwan potyvirus?

[silken]

I will be interested to see what you find Camille. I never had mine tested because I didn't have access to testing and it was so darn contagious, it didn't matter what it was, I had to get rid of them to stop it. Mine weren't in contact with each other either. Just on the same table or nearby. I have also heard it or similar referred to as Taiwan yellows. So maybe it is more of a fungal or bacterial thing than virus. Google that and you will see similar looking leaves as well.

[camille1585]

One way or another, I'll get an answer. If it's not virus I'll see with some people I know in the phytopathology dept if they know where I can send samples to try to identify bacterial/fungal pathogens. Or I'll take samples to work, surface sterilize, grind and plate on nutrient medium to see what grows. Though I think the nutrient mix I have is not generalist enough so it may not give useful information.

[Leafmite]

I love your proposed action! What I hope you will do is take pictures and, when you find the solution, make a post about it to help others, so that they may have an idea what is happening with their orchids.

I agree, all viruses need a vector of some type and plant viruses are not spread through the air. Fungi and bacteria, however, are, and pests can crawl.

As for the cooler conditions suddenly causing issues, that would be in combination, most likely, with some other stress or nutritional deficiency...or perhaps the furnace isn't running as often and you have more humidity. Little changes in the environment can sometimes affect plants.

Good luck!