NOID Denrobium leaves and stems turning yellow

[Floridan by Choice]

I’m fairly new at this and have no idea what is going on. I have researched for a possible answer to the problem I’m having but found nothing. I have gone over the plant with a magnifying glass and found no pests or damaged areas but I guess something microscopic could be going on.

The blooms (just three of them) just finished on this Den, they are still on the plant, wilted, but they lasted 8 weeks (I think this is great) and the plant seemed healthy until three days ago. I have attached a picture of the blooms when they first opened so someone might be able to identify the plant by those blooms. Three days ago, same time I noticed the blooms were at the end, I noticed some yellow mottling of the leaves. Yesterday, they were even more yellow and today even more yellow. I have four other Dens, but all with white blooms, and none of them mottling in the least.

This is not a new re-pot, no pests visible, not over watered – if anything under watered – and I spray every couple of weeks with either Neem Oil or Thiomyl.

We have been having very cold nights for the last week or so, down into the 40s, but I have been keeping them in a little lean-to hot house at night and the temp in there never got below about 55 degrees.

Could this yellow mottling be from the cold or can anybody spot something else that might be going on. Maybe this is one of those species that drop their leaves? Any help would be appreciated.

[NYCorchidman]

Hello, Cecil,

Your dendrobium hybrid is ever green.
I thought microscopic pests as one of the possibilities, however, you mentioned that you spray on a regular basis so that one is out.

Watering or cool temperature is also out since you talked about it, and also the result of overwatering or exposure to too cool temperature on these plants will be yellowing of leaves without the mottling.
just plain yellow, then drop.

This kind of mottling on the leaves can be caused by fungi or virus, and is seen quite common among this type of hybrids along with black spot diseases.

The whole thing will turn yellow and die eventually.
Move this plant away from your other dendrobiums.

[WhiteRabbit]

Hmm... I've had this type drop leaves from being too cold, but if they haven't been under 55 , I don't think that's it. Have you checked the roots?

[silken]

Isn't this one of the Phal or Biggibum type? I thought they were quite warm growers. In that case 55F might be too cold. I don't know a lot about them. I have several and keep them in a warmer micro climate in winter since my greenhouse is 55 at night which I figured was too cold.

[WhiteRabbit]

Originally Posted by silken

Isn't this one of the Phal or Biggibum type? I thought they were quite warm growers. In that case 55F might be too cold. I don't know a lot about them. I have several and keep them in a warmer micro climate in winter since my greenhouse is 55 at night which I figured was too cold.

Mine take overnight lows to low 50s without issue, but I suppose some could be more sensitive than others. I only have bigibbum and two hybrids...

[silken]

Good to know. I really figured these needed warmer temps.

[WhiteRabbit]

Originally Posted by silken

Good to know. I really figured these needed warmer temps.

I only had trouble with mine when I left them out too late into fall, getting down into the 40s overnight - but like I said I only have 3 'mini' types, so don't know if that's any different than the big ones

[NYCorchidman]

These hybrids do need very warm temperature.
Hybrids have lots of different bloods in them, so individual crosses and plants might respond differently to lower temperature, but in general they do best when kept warm (hot during the day).
These are truly tropical.

Now, the ones with more biggibum in it are more tolerant of cool nights as some biggibum go through "cooler" than usual dry winter in the wild.

But again, the best is to treat them like tropical if you have hybrids with unknown background.
One way to tell, the skinnier the flower shape, the less tolerant they are to cool nights.

Now, just because they survivied winter fine without dropping the leaves doesn't mean they are really fine. The following growing season will tell. delayed growth and less flowering....

[Floridan by Choice]

As you can tell from the picture below, when compared to the first ones, the leaves continued to yellow at an alarming rate and the mottling just got worse. I de-potted the plant today and the roots looked pretty good, lots of new ones and even though the old ones are root-bound I couldn’t find many bad ones and nothing rotting nor smelling like rot . When I didn’t find much wrong with the roots, I removed the old canes that had been bobbed and found that there was some purple coloring right under the skin of the oldest cane. I was thinking Fusarium Wilt but found no discoloration of the rhizome nor any rotting of anything.

This Den was one of my yard orchids (could have caught anything over the years that just started acting up) and since I couldn’t find anything on-line that pin-pointed what its problem could be and not wanting to just watch it die one leaf at a time – or run the possibility of infecting another orchid. I just trashed the whole thing – even tossed the pot. Believe me, it was a hard decision to make.

[Orchidreamer]

Could be nutrient deficiency...how often do you fertilize? Could also be a virus, but you won't know for sure without a virus test.