Densrobium help! Dropping leaves!
 

Hi everyone. I recently received a drendrobium with two keikis. I repotted on and left the other one on the mother plant. All the leaves on both plants have started dropping on me. They grow in a south side window and watered once a week when the roots are white.

Thoughts on how I can keep them alive?

Once a week may not be enough. What are your day/night temperatures? Humidity?

The photo is a little fuzzy. Spider mite can cause this, too. Is there very fine webbing under the leaves? If you rub under the leaves with a tissue, do you see red or brown streaks?

I second the spider mite concern.

Also: did you repot the mother plant as well as the keiki? These sometimes dull and drop leaves after repotting especially if the roots were damaged.

you cannot get away with watering a bare-root dendrobium just once a week, bare-root orchids need daily watering.
Since it provides lots of air which is essential to roots it is a good method but some even water 2 to 3 times a day in the height of summer as you cannot overwater growing bare-root but they can dry very easily with this method.
The signs of dehydration is to lose it's leaves like yours is.
If you can make it keep at least 2 leaves then there is hope it will recover.

edit: I see you are down to 1 leaf only already...

First, Welcome!

Do increase the watering frequency... also, as spring approaches you are likely to get new growth. And these are quite capable of blooming on leafless canes so don't cut anything that isn't totally brown and shriveled.