Phalaenopsis with white spots on leaves
 

I just noticed white spots on many of my Phalaenopsis's leaves. I am wondering if these spots are due to disease or sunburn. The plant already has a large sunburn on one leaf (from several years ago). If it's a disease, I'm not sure what it is since the spots are white (at least for now).

I recently re-potted the plant. The photos are of it in its new pot. The medium is Phalaenopsis Monterey Dark Imperial Orchid Mix by rePotme. It had been in a room with south and west facing windows--all windows have shades. I have a smaller Phalaenopsis in the same area, and it does not have any of these spots. I moved the one with the spots to my living room/dining area, which has north and south facing windows, but is less bright. For reference, I live in northern California (Bay area).

The roots look healthy, and it has a new spike.

Look at the underside of the leaves with the light spots. It is very possible there is scale hiding there. If you see white stuff, you can clean it off with rubbing alcohol (70%) on a tissue ore cotton swab. Then best to spray with insecticide like Bayer's Advancee. Soapy water can help. But keep an eye on it... one treatment won't get eggs, you have to retreat about once a week for three weeks at least to get successive generations.

Hi Roberta:

I checked under all the leaves, and there's no white residue and I didn't see any bugs. All of the spots are smooth, and are more see-through than white. Should I still treat it as if it's scale?

If leaf is thinned in those spots, thenlikely not scale, no point in treating for it. I wonder about bush snails. They are tiny snails (less than 1/8 inch, .25 cm) that hide in the medium. They are so small they can't take a real bite out of leaves, but they skim the surface off making thin spots. Snail baits don't do much against them, the only thing that works at all is repotting. Look carefully after watering, sometimes that causes the little beasts to show themselves.

Maybe someone else on the Board has ideas on this.