At this point, nothing. Keep an eye on it. If it should turn pussie, cut it out, maybe the whole leaf. Moonshine is noted to turn brown spots and puss spots when given direct sun, but I lost one to this 'what ever it is'. It traveled down the stem and rotted the crown out. Keep on the warmer side if possible.
Stush

Hi Eugene,

If it were mine, I'd cut the offending leaf off, just in the hopes it doesn't spread.

This is the only leaf, so if I cut it, I lose my only S. Moonshine. It's rooted, but no baby popping out yet. I'll wait and watch.

The yellowing has spread across the whole width of the leaf, and on the right where it started it's now dry / desiccated / dead. The leaf is dying, unfortunately. Shall I pull it out or leave it and hope a baby is growing under the ground, is not going to be affected and is going to survive? Thin chance, I think. I'd throw it away in a second if it was more common, but I really like the look of that Moonshine!

Sorry, but I'd toss it. I believe Moonshine shows up at the Big Box stores sometimes.

Greentoes, Sorry but I have to agree with everyone here Because RUST always spells death no matter what it is and that leave looks really bad, , So just cut it off and hopefully none of the other leaves are affected with it.

It's a nice looking plant other wise maybe to much water but all the other post suggest cut it off and move on.

SO WHY IS THE SANSEVERIA LINK SO QUITE???

Greg

I went to pull the leaf out. (To remind everyone, it's just a rooted leaf; I was waiting for a baby to pop up from under). When I pulled up on the leaf, there was significant resistance - not the "rooted leaf" sort of resistance, but felt like "there's a rhizome in there" sort of resistance. So, I cut the leaf off close to the ground instead of pulling harder. Hoping maybe there IS a baby growing under ground.

Is this sort of rust likely to transmit to the baby? If it's overwatering (which is quite possible), then no, I guess. Can it be fungus?

Green,
If I remember correctly, yes, rust is a fungus.

Planto

So then shall I try to dig out that rhizome if the pup potentially growing off it is definitely contaminated?

The value of the other Sansevieria in the same pot is lower to me than the value of the potential Moonshine pup - but of course if the pup itself is guaranteed sick off of that leaf, then I should throw the baby away.

What do you all think?

Greentoe,
I have leaves that turn brown and I cut them off all the time. No ill effect on the main pant. It just grows more. If you have a rooted bottom to that leaf, and if it has a tiny pup trying to grow, you will kill it if you disturb it. Nature can and does deal with this problem all the time.
It was not know why in the first place it started to die? Maybe overwatering. If so then the roots died first any way. Can't judge by only a picture.
Stush