Phalaenopsis with brown spots under leaves leading to yellowing and leaf death

[Jax79]

Hi all! Can anyone help me identify what’s going on with my phals? On a number of my plants, the undersides of the leaves develop mottled brown spots, then the leaves turn yellow and fall off. The roots are in great condition. This is only happening to my phals, none of my other orchids are affected. I’ve treated with physan20, but am not seeing any improvement. Thanks for any help!

[Dimples]

We need more info about your growing conditions.
Humidity, temperature, how do you water, those types of things.

[Jax79]

Originally Posted by Dimples

We need more info about your growing conditions.
Humidity, temperature, how do you water, those types of things.

They’re grown in north facing bright windows, temps remain between 72-78F currently, less than 50% humidity, and they’re watered when they’re almost dry. They’re grown in bark with some sphagnum, and are fed every other week at half strength. Two of the phals that are having this issue have been in the same conditions for over 5 years, so it’s not likely a problem of growing condition. Thanks!

[Roberta]

When was the last time they were potted?

[Jax79]

Originally Posted by Roberta

When was the last time they were potted?

They get repotted every 1-2 years depending on the condition of the media. Thanks!

[Dimples]

North facing window could be too low light depending on what’s outside. If they’re not getting enough light for extended periods, they’ll have to sacrifice older leaves when they grow new ones.

[Jax79]

Originally Posted by Dimples

North facing window could be too low light depending on what’s outside. If they’re not getting enough light for extended periods, they’ll have to sacrifice older leaves when they grow new ones.

This isn’t normal, oldest leaf drop, it’s on all of the leaves as you can see in the pictures. And again, these plants have been in this window for over 5 years, and they bloom twice a year and have great roots, so light definitely isn’t the problem. Thanks anyway.

[Dimples]

Originally Posted by Jax79

This isn’t normal, oldest leaf drop, it’s on all of the leaves as you can see in the pictures. And again, these plants have been in this window for over 5 years, and they bloom twice a year and have great roots, so light definitely isn’t the problem. Thanks anyway.

I don’t see anything too odd in the first picture. I have phals with darker areas of leaf when viewed from the bottom, especially when the leaf is backlit. Could you elaborate on what you’re seeing and why you think it’s a disease and not environmental. Plants can survive for years in sub-optimal conditions, so extended survival isn’t necessarily proof that conditions are good.

How long has this been occurring? Does it happen all the time or seasonally? Any trends?