Help w/ diseased, yellow leaves

[wieb]

I need some help on understanding why my dendrobium has had two lower leaves turn yellow in a relatively short time (last 2-3 weeks).

And on my cattleya, one leaf has turned yellow during the same time frame.

Please see attached pictures.


Dendrobium, top side of yellowed leaf


Dendrobium, bottom side of yellowed leaf


Cattleya yellowed leaf

If my memory serves me correctly, the dendrobium had some dark spots on them (mottled looking) when they first arrived about 4 weeks ago, but they were green. It seems that when I applied lighting with CFLs about 2 weeks ago, they yellowed much faster. This could very well be coincidental, because I think they had problems to begin with.

1) Any idea what is causing this? What disease?
2) Should I simply cut the leaves off immediately before it spreads?
3) Is there any preventive steps to protect the orchids going forward?

Any information and advice is much appreciated. Thanks in advance.

[robb]

I can't comment on the Dendrobium specifically, but my Phalaenopsis have had several similiar symptoms, in each case the leaves turned somewhat yellow, became pitted and/or veined as your picture #1 shows, then they fall off. all within the span of 10-15 days. Sometimes leaves do it in groups, sometimes singly. It doesn't always kill the plant, as sometimes leaves don't get the damage. I don't know if the Dendrobium and Phalaenopsis would be suffering the same virus/bacteria/insect/fungus/damage/etc being from different groups.

[patlee]

I'm having a problem with one Phal. leaf ,too. You know how the oldest leaf will turn kind of a pale yellow and eventually fall off ? Well, this one started turning yellow towards the tip of the leaf and has been slowly progressing until half of it is little more than a brown and crinkly lost cause. I plan to take the leaf off this weekend so that whatever it is will not spread, but I would like to know if anyone has ever seen or knows of anything similar. Also, the plant has the beginning of a spike--will removing the leaf at this point shock it and make it lose the flowers? I am eager to do whatever I can to prevent this virus/bacteria or whatever from spreading, so any and all ideas will be much appreciated...
TIA!!!

[mayres]

First of all, ALL orchids get yellow leaves that brown/darken and eventually fall off - and fall through winter is a pretty normal time for this to happen. Depending upon the type of orchid, some loose more leaves than others. Many phal type dendrobiums loose many/most of their leaves during this period. Initially people think they are doing something wrong - but this is NORMAL. Don't panic unless it is happening on the newest growth. In most cases, the leaves should be turning brown and falling off on the oldest growths first - on phals the bottom most leaf. Don't worry about cutting them off or pulling them off early. They will naturally fall off or drop with just a touch when the time is right/ripe.
Wieb - nothing in the pics you have shown appear to me to be particularly alarming assuming those leaves are not the newest growth.
Patlee - as long as you are talking the bottom leaf I would not sweat it. Some of my phals loose two leaves per season - as noted above, if so, let it dry and fall off on its own.
If I have mis-interpretted either comments please be more specific WHERE the leaves are on the plant and continue with the pics if possible - those are always good.

[robb]

Well Mike, one of my rescued Phalaenopsis did this, leaf after leaf, all 6 of them, from when I saved it, August 16 until just last weekend, the last leaf fell off at a touch. I am familiar with the leaf aging process you describe, having seen it happen on a few different Phals, but this is definitely some agent at work. I have lost all 3 of my dead Phals to it. Different thread, more details (don't want to hijack this one) so back to Wieb's thread

[wieb]

No, mayres, you have not misinterpreted my situation. They are definitely the bottom leaves (on both the cattleya and the dendrobium). Is it okay to peel them off (damage remaining tissue?), cut them off, or is it better to let them just fall off? Thanks for the assurance.

Mayre, you used this phrase above:

Many phal type dendrobiums

Time for another rookie question -- what do you mean by a "phal type dendrobium"? I thought those were two different types of genera.

[brookn]

Hi,

Phal type dendrobium refers to the type such as yours that do not generally lose their leaves in the winter, and do not need a true resting period in the winter such as a nobile dendrobium or nobile hybrid. I cannot remember all the details presently (sorry) so someone else will have to give you more specifics ( I have worked a lot lately, and exhaustion makes my brain kinda fuzzy).
I do know that when Catts lose leaves it can mean they are in shock, they generally do not lose too many. I cannot tell from the pic very well, but it doesn't look like a sheath which sometimes brown and dry (I could be wrong that it is not a sheath). If the leaves on the Dend are on the oldest cane no big deal, but if they are not, you might want to check for bugs. I would do a careful inspection of both plants for sure. There is a good thread by Cynthia in the pests and disease section.

[pikevi]

mayres is right about yellowing, I think, in wieb's case.

robb: your losing 3 phals ,one losing all 6 leaves, may not be a normal process.

Unless there is a problem of infection, 'excess' water may be a culprit. It may not just be over-watering but could also be water retention in the (bad) medium.

Did you have those re-potted after purchase?

[wieb]

Thanks for sharing, Brookn. And, no, it is not a sheath that is turning brown/yellow.

[robb]

pikevi: all the plants have been treated with the same watering/fertilizing regimen, and were all repotted from a packed moss to an orchid bark mix (Schultz's). It has only happened on a few of the plants, so I am suspecting a virus or similiar. I'll be updating my Survivor: Phalaenopsis thread by the weekend, look for some pictures and details there.

[Cynthia, Prescott, AZ]

Wieb, it looks normal to me too. Personally, unless you have to make something look good NOW, I'd let them fall on their own. Don't need to sterilize tools for that.

For the Phals, are you avoiding neem oil and other horticultural oils? They have caused so much other damage, I would not be surprised if they didn't cause Phal leaf fall too in particularly susceptible plants.

Weib, the terms Phal type (or warm growing type) and nobile type (cool growing type) are named after the two species Den. phalaenopsis and Den. nobile, which characterize the culture of the two types, and are usually heavily represented in the parentage of hybrids of the 2 types. Dendrobium phalaenopsis gets its name because the flowers are shaped like a Phalaenopsis flower. No actual relation other than the flower shape exists between Den. phalaenopsis and the Phalaenopsis family.

[wieb]

Cynthia,
Thanks for the response. I will just let them fall off on their own ... no rush.

I am not sophisticated or knowledgeable enough in orchid culture to try any special oils ... and that may be a good thing, at least in this case.

[pikevi]

Thanks, robb.

I hope it would not spread to the others.

Looking forward to the update.

[orchid_girl]

It does look normal to me too. My dens have all lost some leaves in the last few months. At first I was concerned then I looked around and none of my others were affected. I came on here and did some research on previous threads and found out that it's normal. Thank goodness for this site