Cold damage in cattleyas?
 

Most of my cattleya plants are with spots ranging from purple first to brown and black later. Only a few nights, the temperature has been between 40 * and 45 * F. We have not really had a strong winter and my plants have always been kept outside in other years. How can I follow up on this?

Merita - does this mean that these cattleya plants developed the dark patches while inside the house?

If it is a cold-temperature-related issue, then getting the situation under control should involve shifting the plants to a growing area where the temperature stays within safe limits all of the time. And then allow the orchid to recover. The patches will remain, but hopefully those region dry up - and then will stay very dark for a while, and then maybe change (in the future) to a dry tan/brown colour.

These plants are outside, under the trees, behind the house, they have always been there. I do not know why this winter they are so susceptible to cold, I imagine that something I am doing wrong or maybe sudden changes of the day and night with a lot of humidity too.

Merita - there are reports of some cattleyas being able to handle relatively low temperatures - even down to mid 40 fahrenheit.

But then there is the uncertainty of just how much a particular cattleya can handle ----- and statistics, such as whether some years may have extra high sunlight intensities or extra low temperatures.

Normally, if the plants are grown within safe limits all of the time, then we won't encounter those effects. But if quantities move out of the envelope for safe growing, then we can encounter situations like that.

Merita - on the other hand ...... if taking a chance is allowed (aka betting), then it may be possible that those catts might be able to take some of the cold-hits. This means that they'll come out bruised, but will just keep on growing (despite getting permanent battle scars).

Also, sometimes the conditions might not just involve absolute temperature and humidity etc, but also rates of change ----- such as how quickly temperature fell (or even how quickly temperature rises - such as very cold, but then gets warmed up by sun at a fairly fast rate).

I agree with you, this winter has been different, although I still think that the plants are susceptible to everything because I cannot give them an hour of sunshine with low temperatures, in the morning.

Merita, It is hard to tell, but photo 1 the top leaf looks similar to sunburn, and the under leaf looks more like cold water damage. If cold temperatures were the only culprit here, I believe that the flowers would bare the brunt of the damage and they look pretty good. Once again it is hard to tell from just the one picture.
The second photo is hard to tell what is going on there too. Is it shadow or is it damage on the leaf? That bud should tell you if it was cold damage or not. If it blasts then probably cold, if not probably something else. Cattleyas usually can take fairly chilly temperatures. Lower 40s they should be good, maybe even upper 30s, you maybe OK if the plant is healthy and mature.
The third photo, I don’t know if that is cold damage, looks more like one of the leaf spot funguses. But again it is hard to to tell from one photo. I would ask others in your area or at your local society, if they have had similar damage on their cattleyas due to Cold temperatures. All of these plants look as if they will be mildly effected by this and should recover. Make sure to watch for bacterial or fungal out breaks in these damaged areas in the next few weeks.

All this has happened in the last weeks, first they are purple spots and they become like this, some darker than others; the tips of the leaves and the edges of several plants are getting like this, I have noticed that for the part that gives more cold air, they are more burned. Cold nights continue with a morning of 99% humidity; I do not doubt that some sunbeam will also enter through a corner. I am constantly watching but always have been. Last year there was colder and nothing happened to them, maybe they have calcium deficiency, I plan to put this on these days. Here I do not know anyone who has orchids and I am very afraid that some disease will sprout, I have only been applying hydrogen peroxide in the spots, once, they have not been enlarged at the moment.

You sure could have a calcium deficiency which can cause the plant to have weakened immune system. Making it more susceptible to environmental, bacterial, fungal damage. The amount of sun shine that would normally not cause any harm, now with the deficiency and the cold temperatures, that amount of sun shine could cause sunburn. Also cold temperatures and high humidity make leaves susceptible to many leaf spot fungus, as leaf surfaces stay ‘wet’ longer. Unable to shed excess moisture, and without adequate air movement, the leaves can not defend themselves against some of these pathogens. You say that the damaged spots are not enlarging, this is good, the cause of this damage has happened, as you say, in the last weeks, the enviroment, (temperature, humidity), now has changed and the pathogens are no longer able to survive. Your plants should recover over time. The cold, even if no damage is visible, will stunt or slow down growth. So they will take extra time to restart to grow and bloom.

Merita - is that plant the same one as in this post here?

Any chance those leaves were wet and cold at the same time? Dry Cattleyas are fine with those temps. Wet ones can suffer.