Dendrobium bracteosum

[Dorians grandma]

Hi - I've had a white bracteosum for several years that has always done really well. It bloomed several months ago and grew a keiki, which I have removed and potted. At around the same time, new growth also started. It's about four inches long now and seemed fine until the other day when I saw that the newest leaf had died. The other leaves now seem to have become stippled (have included a picture but don't know if you can really see the lighter areas). I've isolated it but am not sure what else to do. Does it need to be sprayed and, if so, with what? I would appreciate any advice. I really don't want to lose this plant.