Why is my Oncidium twinkle flower spike turning yellow?

[Wade Coleman]

I have an Oncidium twinkle fantasy that has been working on 4 flower spikes for what seems like an eternity. Slowly, but surely, they’ve been growing taller and branching out very nicely, but I began to notice that one of them has begun to turn a straw yellow color towards the upper half. The lower half is still green and branching nicely. What could be the cause of this? Should I cut the spike down to where it is green and let the lower half grow? In the photos you’ll see a picture of the questionable spike compared to a healthy looking spike.

[Ray]

Maybe the plant just decided it didn't have the reserves for that one.

or...

Maybe that spike was exposed to something it didn't take to.

[MrHappyRotter]

Tell us how you care for it and what your growing conditions are like, as well as any possible recent changes. Without specifics and details, we're really all just guessing and there are so many potential causes it's hard to really list them all.

Could be disease, lack of water, rotting/sick roots, poor fertilizer, inadequate light, too much light, wrong temperatures, mechanical damage, critters, etc.

[Wade Coleman]

I have it growing in a south facing window, so it gets direct filtered light all day. I’ve had this guy on a schedule to be watered every 3 days for about a year now. I recently ran out of fertilizer and am waiting until I can order more, so that could potentially be the problem. He hasn’t gotten any for several weeks now. The temperatures have gotten cooler, but nothing too extreme. Upper 60’s at night and mid 70’s during the day. The plant itself is very healthy. The pseudobulbs are fat and green and there is no sign of root rot that I can see. The leaves are nice and green with very minimal spotting. My guess would be the recent lack of fertilizers.

[rbarata]

If you stop fertilization, especially nitrogen, it will bloom better. Some people apply nitrogen rich fert. during the growing stages then stop and apply a phosphorus rich one. Nitrogen is used to grow tissue while phosphorus promotes blooming (reducing the nitrogen).

My oppinion is low humidity.