One of my cactuses has been gradually growing a white coating, and the lower outgrowths seem to be shrivelling up and fading, I first noticed this about a year ago and it hasn't stopped no matter what I've tried. I have no idea if it's mould or some type of sunburn or disease but it seems to have just affected this one, which I treat the same as my others that are growing fine. I was considering taking off the healthy looking top part and just starting again from this, but I was wondering what might have caused this or if it is at all salvageable. Any tips or ideas appreciated, thanks!!
I would separate this guy from your other plants for now. Just in case this is sclerotinia or white mold you need to get it away from all plants, soils. If you could wiggle the top of that plant where the white coating is on the highest joint showing the white coating...how firm does it feel? Wait until you've got more answers from my team mates, okay? But do remove that plant until we are able to ID this for sure.
If it wiggles more than a healthy joint, let us know. If this is sclerotinia just one spore could kill all your plants. Otherwise this could be a normal thing for cactus, I am hoping I am wrong. Not the first time I've been wrong. Sclerotinia is one horrible disease. You might have brought it in with soil or store bought plants or someone's home plant. Those joints being the first to be compromised could be showing sclerotinia. Let's hear what others have to say but remove this plant from the room until we ID this problem. Otherwise, if you separate the healthy top from that highest joint you might find these weird rat turd looking things. That IS sclerotinia. If you do that you have to bag everything and anything that that plant has touched or at least use bleach to clean. sclerotinia
It almost looks like normal corking, but when I look closer, the two pads on the bottom right don't look good. It also looks like it is beginning at the joints on the pads further up the stem.
Is this plant variegated? I may be mistaking the yellow variegation for the same problem as below.
The good news is that it doesn't look like an insect problem.
On the main stem at the bottom, it looks like the cuticle is separating from the layer below. This can be indicative of corking or some disease/mold/fungus.
From the pictures the soil looks very rich and too wet. What I see may not necessarily reflect reality, it's just what I see in the pictures. Has it just been watered?
If this were my plant I would:
Grab a good, non-affected pad now to root in case whatever this is spreads. The get some anti-fungal/anti-mold spray and soak that thing. Moving it away from any other plants is probably a good idea too.
Keep us posted, I'm interested in seeing how this progresses.