Yellow and Brown Area on Cattleya Leaves

[TeriMore]

This Catteleya bloomed beautifully but proceeded to develop yellow and brown areas a few weeks later. Can't tell if it is fungus or bacterial infection. I've attached the bloom and the "spots". Can anyone help?
Teri

[King_of_orchid_growing:)]

How much light is it being exposed to?

[TeriMore]

Hi Philip,
I had kept it outside under my covered patio since I purchased it in Feb. It looked like it was about to bloom and the sheath took a month to open up. Then the bloom lasted for about 2 weeks at most which I posted a picture of as well. After the bloom, I put it outside under an avocado tree with partial filtered sun in the morning only. About a week later a found the yellow/brown area which actually is visible from the front as well as the back of the leaf. I sprayed it with Thiomyl but am worried that whatever it is might spread to the rest of my orchids. I have about 25 plants and am a newbie.. Any help would be appreciated.
Teri

[King_of_orchid_growing:)]

Was it ever very cold when you had it outside?

[TeriMore]

Come to think of it, it might have been outside a few nights when it was cold.