Sudden leaf yellowing/browning on two different vandas
 

Hello,

I have been growing vandas for about 10 years and suddenly two of my vandas had a single leaf near the bottom start to go yellowy and brownish in the middle/end of the leaf which I have since removed and then sealed the cut.

The temperatures have dropped recently because of autumn, it looks like some kind of infection to me but I am not sure. The rest of the plants look completely fine except the one leaf on each that gained this issue.

Does anyone have any thoughts on what and why this occurred? There does not appear to be any bugs after close inspection but please let me know if you have experience with this.

I don't believe the dark parts are sunburn because it ends in a straight/diagonal line with purple tint on the border.

(the mess on the paper is excess cinnamon)

Thank you!

How cold was it in the room? Most people advise not letting them get below 55 F / 15C.

How old is that leaf? It could be a very old leaf dying naturally.

The room never gets colder than 18c its a normal house room and they are not the lowest leaf on the plants. I ve been growing vandas almost 10 years, its not temp damage. The brownish parts are also a bit squishy.

There are two different leaves in the pic, one has wet streaks in it and the other has browned in the middle which is not typical of old leaf dieback.

In that case I would remove the leaves well below the damaged area and watch to see what happens. It looks like you already did this. I don't use fungicides unless I know which fungus it is. Not all fungi are susceptible to all fungicides.

An update on one of the affected vandas, one of the other leaves has begun to develop a brown area at the base/stem and there is a yellow streak developing along the leaf. This must be a virus or fungus. Does anyone one have any thoughts on what it is and how to treat it? Also so you think it could spread to my other vandas?

While one can never determine the presence of virus withou testing, this doesn't look like a virus symptom.This is a fairly old leaf. If the plant is lacking a resource (such as water) it may shed older leaves as a conservation measure. In your location, growing Vandas is going to be a challenge unless you are growing in a warm, humid greenhouse (with supplemental lighting(. In the house, it's always a compromise between what the plant really wants and what you can provide.

old leaves die from the last leaf up not one up, ive been growing them 10 years with no issues since this. I've only had this one a year and its showing this condition. There is also no lack of water. They are all dunked in buckets and fully soaked with no sharing water. They bloom twice a year each for me. I have 20 vandas.

what makes you think its not a virus? when an old leaf dies on a vanda it slowly yellows with no dark brown wet mushy spots at the base which spreads further along the leaf and up the axis of the stem/growth point. old leaves dry up not go mushy.

vandas rarely drop old leaves and not at this rapid pace unless there is something wrong with the plant (weakness, genetics, virus etc). If it was a phal then it wouldn't be such a worry but this is not normal vanda behaviour.

The only way to determine a virus is to test... I have had a few virused plants, the main sign is overall failure to thrive. Most often they have necrotic streaks or spots but not always, and other things can cause similar symptoms. But I have also had plants that showed a positive test but looked good (I do test plants before I give them to other people, otherwise those hearty ones would not even be caught) Can you get test strips? In the US we have Agdia, but I actually get mine from Rega Biotechnical in Taiwan, lower cost per test, the downside is that the minimum order is 50. (They ship all over the world) Perhaps you know other people who would also be interested in sharing in an order if you don't want to get 50. The tests do have long shelf life, I have found them to still be reliable several years after the expiration date, don't need refrigeration.
CymMV + ORSV | Plant Virus Rapid Test | Regabio

I don't know if the test strips are available in the uk, I would have to look further into this.

This issue is something I have only experienced with this vanda and one a few years back and both were newly acquired plants. I wonder if it could be as you mentioned, something like failure to thrive or bad genetics or a bad individual or maybe the transport was too much of a shock to it and its just been too much for it to handle.

I thought it was a virus because two of my vandas showed this symptom at the same time, one recovered but this one seems to be progressing further.

The vanda that had something similar to this a few years back just slowly gave up and the brown progressed from one random leaf at the base by the axis and then travelled up the stem.

Thank you for your advice.

Another reason to not suspect virus if some recovered... plants don't recover from it, they just keep declining. (There is no cure) So I suspect some other sort of infection.