Problem with Psychopsis mariposa 'Green Valley'
 

This is my only Psychopsis and I hope she won't be soon departed. Just a few months ago, she developed some yellowing on her oldest leaf which has now subsequently turned brown - but yet is still very firmly attached to her pseudo bulb. She has three spikes, all bloomed a few months ago. She currently has two spikes in bud but the brown leaf p.bulb one has no bud. Now, to my horror, just today, I noticed that another two of her leaves are yellowing. Is it, could it be ... sunburn?? Hopefully ...

http://i1216.photobucket.com/albums/...psjv9fvjjr.jpg

http://i1216.photobucket.com/albums/...psjhrr1qjz.jpg

What are your day/night temperatures, humidity? What kind of light? How are you watering?

It's out of focus, but at the base of the pseudobulb in the photo with the brown leaf - do I see white cottony material?

Sorry about the poor quality pic but that white dot is diatomaceous earth. My day temps are high right now about 34°C and night time is probably only slightly lower. Current humidity is high - ish about on average 50°C to 65°C. I grow her on a south facing window. No shade.

I have had her since 2012 so she has weathered many storms with me. She was fine, really great root system. I just can't think.

I suspect it's from heat and sun. Maybe move it back from the window a bit.

I wondered if it was heat damage but either way she is not going to bloom again until she makes a new pbulb. Thanks for your replies.