Yellow on cattleya pseudobulbs and leaves

[CindyBallard]

I am a beginner forum member and a reasonably new orchid lover. I have a shadehouse with about 60 cattleya and still have so much to learn. I have been really pleased with how they are all growing and responding to date, although I have now learned that my shadehouse needs to move to a full sun position so I will tackle that big job when I can. This is the first real problem I have encountered. I went in to 'talk' to my orchids a few days ago and was alarmed at the yellow on some pseudobulbs and a bit of yellowing on the leaves. I have racked my brain and I think I may have been using a stronger than recommended dose of fertilizer. Could this be the problem? It is all that I can think of however not all of them have this problem and my 6 phals. that live on my back deck have not showed any ill signs and neither have any of my others (4 vanda's and about 10 dendrobiums). Any thoughts would be much appreciated.