In Florida, the most common cause for what you are describing, is thrips. You can only see them on open white flowers. They look like a little minus sign and they move fast. On vanda buds you can't see them at all. There's an easy remedy. Get a spray bottle of Ortho Rose and Flower or Bayer Rose and Flower. They're available from Home Depot or Lowes and they're designed to be used on open flowers. When your vanda spikes are 4" to 6" long, spray the spike from about a foot away so you get a nice gentle spray. Spray from two different directions. A week later, spray again. Twice is usually enough but sometimes I spray three times. Don't spray once the buds get mature and fairly large. I've found that it can stain the petal colors of mature buds but it's very effective when used before the buds are fully formed. It works like a miracle for me. Orthene also works well but I don't like the smell of it.
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