What kind of grow medium is it in, and did you make sure it had an 'extra' measure of water to carry it over while you were away?

It looks like oedema/ edema, a physiological disorder. Something I wrote about it:

Oedema

Oedema (aka edema) is a physiological disorder that can affect all terrestrial plants. It occurs when the plant takes up more water than it can rid itself of via the process of transpiration. The word itself means 'swelling', which is usually the first symptom, and comes in the form of pale blisters or water-filled bumps on foliage. Under a variety of circumstances/cultural conditions, a plant's internal water pressure (turgidity) can become so high that some leaf cells rupture and leak their contents into inter-cellular spaces in leaf tissue, creating wet or weepy areas. Symptoms vary by plant, but as the malady progresses, areas of the leaf turn yellow, brown, brown with reddish overtones or even black, with older damage appearing as corky/ scaly/ ridged patches, or wart/gall-like bumpy growth. Symptoms are seen more frequently in plants that are fleshy, are usually more pronounced on the underside of leaves, and older/lower leaves are more likely to be affected than younger/upper leaves.

Oedema is most common in houseplants during the winter/early spring months, is driven primarily by excessive water retention in the soil, and can be intensified via several additional cultural influences. Cool temperatures, high humidity levels, low light conditions, or partial defoliation can individually or collectively act to intensify the problem, as can anything else that slows transpiration. Nutritional deficiencies of Ca and Mg are also known contributors to the malady.

Some things that can help you prevent oedema:

* Increase light levels and temperature

* Monitor water needs carefully – avoid over-watering. I'd heartily recommend a soil with drainage so sharp (fast) that when you to water to beyond the saturation point you needn't worry about prolonged periods of soil saturation wrecking root health/function. Your soil choice should be a key that unlocks the solutions to many potential problems.

* Avoid misting or getting water on foliage. It slows transpiration and increases turgidity.

* Water as soon as you get up in the AM. When stomata close in preparation for the dark cycle, turgidity builds. If you water early in the day, it gives the plant an opportunity to remove (for its own needs) some of the excess water in the soil.

* Put a fan in the room or otherwise increase air flow/circulation. Avoid over-crowding your plants.

Al

Thanks Al. its in a bark mix (Repotme) with some leca and alittle spagnum. Its fast draining. i watered the day before we left so 8 days later i was checkiing them all upon my return to see if they needed watering. i usually water about once a week to ten days this time of year. they are all together in the same environment so im puzzled why only this one and only one leaf, and soquickly. guess Ill just keep an eye on it to see what happens. Thanksfor the info.

If you lowered the house temperature while you were gone, that has the potential of being a contributing factor.

Al

abykaz, I'm not an authority on orchid diseases, but I do see something in your second leaf photograph that does make me wonder. that leaf in the middle photo in your first post seems to be noticeably more yellow on the right end as you look at it in the photo. I believe that is the attachment end. It appears that the leaf is near mature in size, but does not appear to be fully opened out, and noticeably more yellow on the base end. You also say that that leaf appeared to be "weak where it attached to the plant." You may have a rot or fungus problem in the central stem of that plant, and to be sure there's nothing hiding in there I think I would unpot that plant and have a close look at it.

Bill

Yes Bill, your observations are correct, there is that yellowing and there was a flimseyness to the base of that leaf, part of my concern. i will unpot it and have a look. i appreciate your thoughts on it. Al, the house was warm while we were away - the cat likes it warm! :-)

There is some possibility of it being a viral infection too.