Brown Spot with Yellow Leaf on Dendrobium

[NYCorchidman]

It is not sun burn for sure.

When this happened to one dendrobium hybrid I had, I kept trimming off the affected parts of the leaves because I really liked the plant and wanted to somehow save it.
Well, that ring kept on showing up again and again, so whatever the cause was, I just had to toss it to protect my other plants, and I have lots! better to toss one sick plant than to risk ruining so many.

Have you got the lab result back from Purdue??

[SJF]

Originally Posted by KristenJ

Thanks, I have isolated the plant. There was a keiki growing beside it and I noticed a small spot on its oldest leaf. I removed the leaves and applied cinnamon. Both plants are now being watched.

Out of curiosity, I dropped the leaves off at the Purdue Plant Disease testing lab today. I will repost when the results come back in case anyone else has this problem in the future.

Hi,
Did you receive results from the lab?
~SJF

[KristenJ]

Sorry I am so late in responding! The end of the semester was too crazy.

Here is what is happening right now, maybe it will help somebody else who encounters a similar problem.

Both lab tests came back inconclusive. I isolated the 3 dendrobiums (1 adult, 2 keikis) that ended up each showing a spot. I cut the leaves and applied cinnamon on the cuts. I also sprinkled cinnamon on the surface of the potting media. I waited for the results. The first set came back inconclusive with the following report:

"I am unable to determine a specific cause for the leaf spots without more extensive testing. There was no evidence of a bacterial or fungal disease. The green halo remaining around the leaf lesion as the remainder of the leaf turns brown suggests a possible virus, but it is not typical of any specific virus I've seen on Dendrobium. Serological tests for Cymbidium Mosaic Virus (=Odontoglossum Ringspot Virus) and for Cucumber Mosaic Virus were negative.

To further explore the possible involvement of a virus would require sacrificing much more plant material and electron microscopy work. Other diagnosticians in our network were not familiar with this symptom either."

About a week after I got these results, I noticed new spots (on 2 of them). So I cut these leaves & brought them in that same day. The second report was similarly inconclusive:

"Again with this sample I found no evidence of a bacterial or fungal problem. This may be viral but the symptoms are not typical of any known virus. This could be a nutrient problem, but that is just a guess. I think we would need to see this on several plants of the same type simultaneously in a commercial grower's greenhouse to have enough material to send for electron microscopy examination of possible virus particles. I'm sorry I can't be of more help in this situation."

Since these are small dendrobiums, I did not have enough plant material for further testing. When I noticed the second spots beginning, I ordered Physan 20 on Amazon. Since then (mid April), I've been spraying the 3 of them every 2 weeks. So far, there has been no further spotting. D. Gending is growing a new cane with no problems. One of the keikis is growing a new cane but currently losing a lower leaf with no spots. The other keiki is struggling to grow a new cane because it was so small when the spots started that there were only 2 good leaves left on the first cane and it has since lost 1.

I still have them isolated. I have no other problems with any of my other orchids so far. Concerning a possible nutrient problem - I don't know. I use FeedMe MSU formula from RepotMe on all of my orchids and they all seem to love it.

Sorry there was not a definitive answer to this problem!

[NYCorchidman]

Thanks for respongding!
I hope you finished the semester on fantastic term!

Regarding the dendrobium issue, I do not think the ring thing is due to any nutrient deficiency, and here is why I think that.

I grow all my dendrobiums the same way. Only two were tossed due to the ring issues.

I have quite a few dendrobium hybrids. I have tossed two that showed the mystery rings.
One was affected to a point that all the canes went bare. The other one was severely affected and I kept trimming off the leaves. well, eventually I tossed them. It looked bad. and worried me too much.

Now I have one dendrobium doing the mystery ring at the moment, which is a nightmare coming back to haunt me because I love this one and is not common.

I haven't trimmed off any leaves yet and I'm just watching with careful and worried eyes.

I think it has to be dendrobium virus of some kind.

[KristenJ]

Thanks!

It figures that I post all has been well and something would go wrong lol. The other keiki showed another ring a few days ago and dropped the leaf. I am continuing to spray with Physan.

I hate to jinx myself, but it seems like it has worked for D. Gending. This one was first to show symptoms but only lost one leaf and has had no problems since. The keikis continue to struggle.

I am inclined to think it is a virus as well. And that the younger plants are not strong enough to deal with it.

[mjf45322]

Does anyone know of any testing lab in Ohio where I could get some of my plants tested .

[TOMMYMIAMI]

Juts of the curiosity - what happens to all the dendrobium leaves at the end of summer and fall, when they are loosing them because they are preparing for the winter rest??? As I do understand it, there is huge amount of deciduous dendros that will loose leaves, starting now till fall, before their dormancy stage. Can this be the sign?

[NYCorchidman]

Well, it is too much to cover them all here and it is rather irrelevant.
You might want to start a new thread on that if you'd like, but let me say one thing: the ring thing that has been discussed here is not part of natural discarding. It is definitely a disease.
I have a few nobile hybrids. When they lose leaves in the fall (or anytime they want to), they just turn "clean" yellow and fall off. no rings or spots of any kind.