Phalaenopsis with suspicious yellowing leaf

[TER]

Hi,

my Phalaenopsis mannii has been doing just fine until now.

I watered it 5 days ago, and I noticed nothing suspicious on the leafs, but today a middle leaf is getting suspiciouslly yellow.

I don't have enough experience to tell what it is. I have been wanting to repot because there's a lot of alguea in the pot due to the exposure to light, but it has been in bloom for quite some time and I have not wanted to mess with it. I now wonder if I should.

I have taken some pictures. Could you please take a look and help me understand?

Thank you.

[Ray]

First of all, algae in the pot is of no consequence. Light+moisture+fertilizer=algae growth.

Normally, a yellowing leaf is a sign the plant is extracting the nutrients for use elsewhere, but that usually is the oldest leaf first.

A sunburn can also start as yellowing, but the little spots in that image make me wonder if it might be an infection that is secondary to an insect issue.

I don’t see a lot of roots in that pot, do you have any idea of their condition?

[TER]

Thank you Ray.

I thought of an insect too, but you mentionning roots, rang a bell. I have noticed that it has grown mainly aereal roots and it was attached only at one point.

So, I have unpotted just now and in the vase there weren't nice roots. The longest is attached to the stem by a very withered thread, although at the bottom it is green. Should I keep it?

I don't know if this is the reason for the yellowing, but it must make it weak and more susceptible to infections.

[Dimples]

The roots from the pot don’t look that bad. They aren’t brand spanking new, but they look plenty functional. Phal roots will be green if they’re exposed to light. If they were in the middle of the media they’ll often be yellow/brown/tan from being in the dark. Older roots can also develop a brown or off color hue from age. Small spots of withered velamen (not uncommon on the exposed parts of older roots in dry environments) aren’t anything to worry about and the root can still function normally.