Dendrobium nobile with aggressive soaking brown rot on new leaf tips

[mvmgems]

Hello everyone, first post and two-month newbie.

I recently got my first non-phal, a Dendrobium Wave King “Akebono.” It seemed to be doing well except for one mature mealybug and some black/brown speckles, with a steadily growing new shoot and roots. Then nursery had potted it well in a slotted clear plot and small bark/perlite mix.

This orchid lives close to a partially shaded southwest window getting a few hours of direct sunlight. Temps indoors are 68-78F right now, and humidity 35-40%. I water every few days when the oldest psb starts looking a bit shriveled, alternating between tap/RO water and quarter strength MiracleGrow Orchid Food + quarter strength Superthrive.

I’m still in the honeymoon stage with orchids so I inspect them several times a day when I’m at home, which was most of the last week. Thursday, I noticed that the largest leaf on the new growth looked like it had a waterlogged brown tip, and frantic googling told me it was probably bacterial soft rot. (Photo 1) I excised it with alcohol sterilized scissors and a ~5mm margin, then dusted ground cinnamon.

Saturday, I noticed the middle of the cut appeared to be getting waterlogged again, so I cut it this time 1cm past the visible damage. (Red line in photo 2 approximates extent.)

I looked over the orchid this morning and it seemed fine, then went out for the day.

Came back to another leaf tip with a circular waterlogged brown spot 1cm deep. (Photo 3) I actually have a pic of it the day before looking fine (left most leaf on photo 2). Cut that one with the same treatment as last time. I’m going to run out of new leaf at this rate! (Photo 4).

Am I doing something wrong to increase its susceptibility? Can I do something more to prevent this?

[estación seca]

Welcome to the Orchid Board!

Fungal and bacterial rots are uncommon at lower humidities, such as you report. I don't think that is your problem.

It might be residual damage from where bugs bit the plant. This kind of necrotic spot can happen at those points.

Most Dendrobiums, especially nobile hybrids, need lots of water during the growth phase. They should not become water stressed at all or the newest growth may die back. I would not wait to water any Den. in growth for pseudobulbs shriveling.

I can see linear shrivels in at least one leaf, which is a sign of insufficient water. This would suggest either the roots are in poor condition, or you aren't watering enough. You've mentioned the roots are growing well, so this is unlikely to be the problem.

In a slotted pot at your temperatures and humidities, the root mass may dry out quickly. I wouldn't be surprised if you needed to water every 1-3 days. In a very well-aerated mix you could water a Den. nobile hybrid in active growth daily.

I agree with cutting off the leaf tips, and watching to see whether the necrotic area advances.

[mvmgems]

Thank you very much! The article I read said that Dendrobium nobile likes to dry out more than Phals because they have psb, but perhaps it was mistaken or this particular one wants more. I wasn’t sure what to look out for.

[estación seca]

Have a look at this thread:
Need Help with my new*Dendrobium Wave King Akebono

[mvmgems]

Thanks for the additional link!

Next leaf tip up showing the same damage. Photos taken one hour apart - this is a speedy one! So far the cut leaves look okay.

Keeping an eye on this translucent area at the base of the oldest leaf on this shoot too. Whatever this is, it’s making me paranoid.

[Leafmite]

Sometimes you can stop this from spreading by wiping the plant (everything but the roots) with isopropyl alcohol. If this continues to spread and you think the orchid is in danger, it might be time for a systemic fungicide. Here is one:

https://www.amazon.com/Southern-Ag-O...052OHF9I&psc=1

To prevent future infections, extra Calcium while the orchid is actively growing will help build stronger cell walls which will help the plant more easily resist fungus/bacterial attacks. Good luck!

[mvmgems]

Thanks for the suggestion! I just ordered MSU which has calcium and magnesium in it, unlike my current miracle gro fertilizer (and Ca/Mg seems to be a whole rabbit hole I’ll dive into later.)

In the meantime, for science, here’s the progression of the cut leaf tip one hour after I noticed it (right after cutting), and then 6h after that. Temp in low 80s.

[Shadeflower]

That is fast progression.
Luckily I don't think I have experienced something that aggressive which would make me paranoid too.
I'd go with what leafmite has suggested.
All I can add is that I have always hated miracle gro - always considered it to be toxic goo myself so I'd always recommend to ditch the miracle grow but whether the miracle gro is causing this is hard to imagine but who knows. The glowing blue fluorescent color of the fertilizer never convinced me their ingredients were safe let alone organic

and just to make sure I am not just voicing my personal opinion(well it is but at least I am not the only one)

The Reasons Why Synthetic Chemical Fertilizers like Miracle-Gro Are So Bad for Your Garden (& Organic Alternatives!) — Heirloom Soul Florals - Wedding Florist and Flower Farm in Buffalo, NY WNY

[WaterWitchin]

ShadeFlower, I'm with you on the Miracle Grow! And it has copper sulfate in it... there are a lot of dendrobium that it's extremely toxic for. No idea if yours is one of them.

[mvmgems]

End of season updates:

I had no further issues with rot of new growth since switching to RO + MSU fertilizer, so I suspect calcium deficiency really was the issue! The new cane has matured with 10 leaves (compared to 5-6 on prior canes). I stopped feeding in August and am watering lightly once a week now, letting the older cane get a little shriveled between waterings. The second oldest cane is now starting to drop leaves, which I think is normal? Fingers crossed for blooms in spring!