Problems with formosae dendrobiums - yellowing leaf tips

[calvin_orchidL]

Hi everyone,

I'm having some problems with two of my dendrobiums. As some of you know, I really enjoy growing the formosae/nigrohirsute dendrobiums. It's now my 2nd season growing them, and while I'm getting fatter/taller canes compared to previous years, I'm also noticing some strange leaf yellowing problems. I've noticed with dendrobiums in general that the 'normal' leaf drop occurs by which the entire leaf turns yellow, then dries and drops off. However, what I am observing is a yellowing from the tips, followed by a drying, that progresses from the tip down to the base of each leaf. This also commences from the bottom of the cane up.

No rot, just yellowing and drying. I fertilize way too infrequently for this to be fertilizer burn. Regardless, below are my conditions and some photos...I'm really hoping someone out there can help me out. These are two of my favorite plants so I'd appreciate any feedback whatsoever.

Plants in question: formosae dendrobiums
Dend Peng Seng (tobaense x cruentum)
Dend Frosty Dawn (dawn maree x lime frost)

Conditions:
8" from T5 lights, 16 hrs a day
Grown in a tank with higher than ambient humidity (vague, yes I know)
75-85F
Potted in 3" plastic pots with course fast draining coconut chunks, charcoal, and hydroton pellets.
Watered once every 3-4 days, media is allowed to NEARLY get dry in between watering. (at the beginning of the summer, I let them get bone dry for a day in between waterings...that was when I started seeing the yellowing, so I upped the watering schedule...but the symptoms are still progressing)

Plant conditions:
In general, roots seem very robust - both plants have tons of roots, growing both into the pot and out of it. All roots have green tips, all look white and healthy. Both are quite root bound, to the point where I could risk some damage if I were to unpot them. It does concern me a little that there is little to no root growth out of the holes at the bottoms of the pots...nor can I see many roots through the holes at the bottom.


This is the plant today - it's been in bloom 2nd season now, for 3 months, on the second cane. It is currently maturing another cane which I believe is near to mature. You can see the severe dying back of the leaves...originally I attributed this to a natural annual leaf drop. However...


the newest cane is now showing some leaf tip yellowing which scares me.


This is Frosty Dawn...started showing the yellow leaf tips about a month ago.


Lots of roots all over the place. Some roots look like they stalled and then came back to life...not sure why.


The new growth on the frosty dawn...lagging behind the peng seng but it looks good so far. You can see both what I suspect is a natural leaf drop (the entire leaf is yellow) as well as the strange leaf tip yellowing in the background.

I'm not sure if humidity is an issue...I suspect not, because I have a dawn maree which is a parent of frosty dawn, and it's growing happily on my windowsill with no yellowing at all.

Any ideas? I've exhausted all my options so I'd really appreciate any leads.

[snow]

just a thought. have you checked for spidermite?
they can go on for a while before the symptoms are noticed. i hope that,s not it.

[quiltergal]

That's very puzzling Calvin. The newest growth on my Frosty started showing die off in the newest leaves but then it stopped and the leaves continued to grow normally. The only thing I could think of is it got a bit too dry. It's blooming, sending up two new growths, and new roots all at the same time. My thought was I wasn't watering enough to keep up with all the activity. It's been in the same spot for the last 3 years, so I don't think it's location. We had some very cool nights earlier in June, and we sleep with the windows open. It might have gotten too cold and developed cell collapse.

I think it might be time to check the roots on yours Calvin.

[calvin_orchidL]

Thanks for the replies!
Snow - I have checked and sprayed down with safers - no improvement.

Terri - I think, from what I've gathered in several forum where I've posted this question that heat and dryness is the culprit. Was it hot when your leaf yellowing happened? I'll have to rig up some fans to dissipate the heat from the lamps to see if that helps.

[quiltergal]

Calvin it was hot during the day but very cool at night. Whatever it was only affected 2 of the new leaves at the top. I thought most of the Formosae section liked heat?

[catwalker808]

Calvin & Quiltergal. Sometimes we only give educated guesses, but this time I think I can give you a pretty good diagnosis and the reasons behind it.

My first concerns would have been roots. But your roots look really plentiful and healthy ... not roots growing out of the pot because of soggy conditions, but really nice looking roots. I have seen your leaf conditions many times. It's water stress probably caused by your long period between watering combined with the hot spell.

Let me explain something about the formosum dens and their hybrids. They do not all react in the same manner to the same growing conditions. Formosum and cruentum are both definitely warm growing, making Dawn Maree also very warm growing, capable of even periods of full sun (although cruentum and Dawn Maree can also tolerate intermediate as long as they are kept from having wet roots and leaves.)

On the other hand, tobaense is rather fussy if it gets too hot and dry. The species and your hybrid only have very few and very slender canes which cannot store very much water.

And Frosty Dawn is another story. Although one parent (Dawn Maree) loves warm to hot and can tolerate drought, the other parent (Lime Frost) has scabrilingue as one parent. Scabrilingue is the species that provides the nice fragrance to Frosty Dawn. However, scabrilingue is also semi-deciduous under intermediate or cooler conditions, especially when available light is lessened as in winter and early spring.

Under such conditions, the older lower leaves on older canes will drop. This is a typical seasonal reaction. Newer canes may also experience slight yellowing on newer soft top leaves, if the environmental conditions change severely.

All of this type of seasonal yellowing or leaf drop, however, is different from the leaf conditions in your photos. With seasonal (normal) leaf yellowing, the leaves gradually turn a lighter green, then slightly yellow, than more yellow ... but evenly throughout the whole leaf. Then the leaves drop. And the leaves retain their moisture for a while. Your photos show yellowing only at the tips initially, then the leaves turn brown and dry from the tips inward, while the lower half of the leaves remain green and intact on the plant. With continued water stress, the entire leaf will shrivel up and drop off.

This is caused by water stress. With your good roots, you will find that if you correct the watering problem while the leaves are sound at least half way down, then the green part of the brown tipped leaves may remain on the plants until they eventually drop off of old age. Just cut off the brown part with a clean blade.

Calvin. You should have asked your recent society speaker about the leaves.

[quiltergal]

Catwalker, thanks so much for your excellent explanation. I will keep a closer eye on my Frosty during the summer season, especially this year since it's trying to do so many things all at once. Normally it blooms in the spring for me, but this year it's blooming in the summer. It could be because we had a rainy gloomy spring. Quite a few of my plants are blooming much later this year than they did last year. Thanks again!!

[calvin_orchidL]

Wow I didn't realize there had been replies to this!

Catwalker - thanks for the explanation! I actually pulled the plant out of the pot and checked the roots and they do seem find. I'm glad you have confirmed my suspicions. I'm adding more water and running a fan to disapate heat, so hopefully this improves things. I did ask Harry Akagi from H&R about this, and he mentioned that it is normal, but I guess I didn't explain the problem thoroughly enough (it was a mad house so I was lucky to even be able to get a word in with him!) and I forgot to bring the plant to show him.

In regards to the tobaense, I have one in the tank, which is the place that gets a bit warm. However, I do have a window sill where I can put it that is much cooler. Unfortunately, the light is not as good as inside the tank (north facing window ). Does the tobaense need the bright light to grow properly? I have one that is in the tank and putting out a new growth/leaves but I am concerned that a similar problem will affect it in the future, even though I am keeping it quite moist.

[catwalker808]

Calvin. I would also have said lower leaf drop of old leaves IS normal for Frosty Dawns when the temp turns cold. That is, until looking at the photos of your leaves half green and half brown. And we had much more info here.

Remember, they invented Frosty Dawn and so many other formosum hybrids. And they have grown thousands of them. We had the advantage of seeing your photos here to make the diagnosis.