Question
I live in South Florida where the temperature recently went down to 36 degrees.  I put many of my well established orchids under a shelter against the house and covered the whole thing with a large blanket.  It is now a week later and most of my dendrobiums are turning yellow with some browning too.  These plants are well acclimated to being outside all year. I put the phals in the garage because they are in bud and they are fine as are cattleyas that were sheltered in the same area as the dendrobiums.  Do you think this is cold damage, a virus?  Thanks for your opinion.

Answer
I doubt that it is due to a virus.  More likely, the combination of cold and darkness has caused the dendrobiums to go into a rest period in which they will lose most or all of their leaves. If the canes are strong and don't show any mushiness, I think they will be ok until they begin new growth in a few months.