Black patterned spotting on leaf and subsequent yellowing on Phal. Mini Mark

[cousky]

Hello everyone.

I have had this Phal. Mini Mark for 8 months, has been doing well except for some spotting that appeared 5 months ago as seen on the first picture. It only appeared on two of the leaves. It seems to have formed a pattern, it is pitted and black, some yellowing and browning following the pattern of spots resembling water staining on wood following the grain. it has remained constant since it appeared and the plant was doing well with new leaf growth, root growth and a new spike this month.

My first question is what could this spotting be? It doesn't seem to have caused problems except for appearance of the leaf.

Second question is related to the yellowing leaf. Started a week ago, on one of the spotted leaves. started with the tip, yellowing towards the crown, the yellowing has now turned soft, indicating decay of the yellow material.

It is facing a window, 30-70% humidity, 20C, live in zone 5, Fertilized with every watering 150ppm N of 13-3-15 RO orchid fertilizer, using distilled water. Potted in an airy orchid pot. Basically, it has been doing well to my standards until this week.

During Winter and Fall, days were mostly cloudy and shorter but lately I have had very sunny days with 2-3 hours of direct light. It is not unusual for some of my orchids, they do not seem to mind the light and I monitor them for sunburn and I havent had any sunburn despite direct light (Except perhaps this time). The other leaves are fine, they receive the same amount of light.

The question is whether this is sunburn or not?

I really appreciate your input, I have done a lot of research through the forum and outside and usually learn through experience, I welcome your questions and criticism.

[estación seca]

Welcome to the Orchid Board.

Was the leaf close to a cold window?

[cousky]

Thank you! Not any closer than the other plants, about 12 inches. Same place it has been during winter.

[estación seca]

I still think it might be cold damage. Consider putting a thermometer next to the side of the plant close to the window to see what the temperatures are.

[FranningtonBear]

Originally Posted by estación seca

I still think it might be cold damage. Consider putting a thermometer next to the side of the plant close to the window to see what the temperatures are.

I agree. I was gifted two Phal’s a couple of years ago, both with yellowing leaves just like yours. Previous owner told me the affected leaves had been near a north facing window. I haven’t experienced any further abnormal leaves since they arrived and were placed in a warmer location.

[cousky]

Update: Cut the first leaf before it yellowed all the way. The part around the stem is still green. The second leaf that had marks on it yellowed the same way. It yellowed and dried all the way down to where the leaf wraps around the stem, without affecting any other leaves or the stem. Tried to remove it, but had to cut it off as well. Orchid is still flowering and looks fine, other leaves look stable

Considering that the second affected leaf started rotting later than the first one, I assume it has something to do with the black marks. These marks appeared and remained static for more than 6 months. I don't believe it is cold damage (however, I do agree that it looks similar to it and it is a probability due to being near a window), since it happened on two leaves facing different directions and the other leaves are fine. Or perhaps it is cold damage on already damaged areas of the leaves, which resulted in yellow rot. But then again, the yellowing on the second leaf didn't start until after the first leaf was already removed.