Orchids forum→white cast on jewel orchid/macodes petola leaf

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Gabi567
May 29, 2020 7:31 AM CST
hi everyone!

I am keeping my macodes petola in a terrarium, which I open in the evenings when humidity is higher to get some air flow. It's a new plant and is in sphagnum moss which I keep moist.

it seems that the plant developed a white cast on its leaf. what could it be? does it need better airflow? It's my first orchid - thank you for your help!




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Name: Big Bill
Livonia, Michigan (Zone 6a)
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BigBill
May 29, 2020 8:02 AM CST
It looks like it could be powdery mildew.
It comes from humid conditions and poor air circulation.

How large is the terrarium?
I know of several people growing orchids in a Wardian Case which is similar to a terrarium. However, the Wardian Cases are equipped with muffin fans. These tiny fans keep the air moving.
Rodney Wilcox Jones, my idol!
Businessman, Orchid grower, hybridizer, lived to 107!

Gabi567
May 29, 2020 8:37 AM CST
Thanks Bill for your help! It's a 30cm x 30 cm mainly decorative terrarium for a 5cm pot plant, it's the only plant in it, but does not have the air flow indeed... Below is a picture of it from the producer, I will keep the main door open often to increase the air flow.

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I have also taken a picture of the roots. It seems that there is a part covered in black residue. I know that the previous owner kept it in an aquarium, could it be some sort of algae or is it root rot? I repotted it into fresh moss with some perlite and very fine orchid bark meanwhile, in case the old moss was causing an issue (it was very wet as well).

Thumb of 2020-05-29/Gabi567/519ccf

Name: Big Bill
Livonia, Michigan (Zone 6a)
American Orchid Society Judge
Region: United States of America Critters Allowed Growing under artificial light Echinacea Hostas Region: Michigan
Butterflies Lover of wildlife (Raccoon badge) Orchids Cat Lover Birds Bee Lover
Image
BigBill
May 29, 2020 8:57 AM CST
Moss does degrade and go acidic. The wetter it is kept, the quicker it degrades. When it degrades it gets acidic which often leads to root loss.

The black discoloration could be mold, it could be fungal or just a discoloration due to anaerobic conditions.
Rodney Wilcox Jones, my idol!
Businessman, Orchid grower, hybridizer, lived to 107!
Name: Ursula
Fair Lawn NJ, zone 6b
Plumerias Orchids Cactus and Succulents Region: New Jersey Region: Pennsylvania Native Plants and Wildflowers
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Ursula
May 29, 2020 9:15 AM CST

Moderator

Do they still sells those small 10 $ computer fans? They would work perfectly in such an environment.

Yes, amazon sells them!
[Last edited by Ursula - May 29, 2020 9:16 AM (+)]
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Gabi567
May 30, 2020 6:32 AM CST
Thank you Bill for fantastic advice, I made sure now that the moss/perlite/bark mix allows more air into the roots as well, before it seemed to have been squished incredibly tightly in very wet moss, maybe for transportation.. I also used a bit of fungicide on the blackened root just in case.

Thanks Ursula, the computer fans are a great shout! I will order one and mod my terrarium!

[Last edited by Gabi567 - May 30, 2020 6:32 AM (+)]
Give a thumbs up | Quote | Post #2257019 (6)
Name: Big Bill
Livonia, Michigan (Zone 6a)
American Orchid Society Judge
Region: United States of America Critters Allowed Growing under artificial light Echinacea Hostas Region: Michigan
Butterflies Lover of wildlife (Raccoon badge) Orchids Cat Lover Birds Bee Lover
Image
BigBill
May 30, 2020 7:15 AM CST
Your welcome
Rodney Wilcox Jones, my idol!
Businessman, Orchid grower, hybridizer, lived to 107!

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