Dendrobium victoriae-reginae -- rapidly yellowing leaves and leaf drop

[drglchrst]

Hi all,

I have been keeping a D. victoriae-reginae until recently. For about 1 year it was living in on a tinted windowsill in a moss-bark mix, watered just when moss became crispy. The plant seemed healthy for most of that year, sent up 2 new canes and flowered twice.

Unexpectedly, the bottom leaves of 1 cane turned a mottled yellow over the course of a day, and dropped the next. Over the course of about a week, this moved up to the top of a cane, and began with the next. At the point when all mature canes were toasted, I plucked a seemingly unaffected keiki and have tried keeping that one alive, but it too is now doing the same thing. Picture attached shows how the yellow mottling looked.

I don't believe the media had been too wet as it was allowed to reach "just about" dryness between every watering, and the size of the pot was not so large that I woulr have expected a wet core.

Any indications what this is? If this keiki can be saved that would be great news, but I would be happy to know what caused this and how to prevent in the future. Best,