Cactus in trouble

[curious physicist]

Help! While repotting, my cactus collapsed and broke into three pieces? I let it sit for a week to calluse over, but the middle piece rotted away, and the bottom piece's top become black and soggy. I have pictures of the top and bottom piece attached.

How can I save the cactus?

Thanks for helping!

[george76904]

The bottom piece that is still rooted looks ok. Let the cactus callus over and then it will be ok p, but the skinny part is an indication that it needs more light. As for the top part. You should take a blade, sterilize it and cut off the rotting part. Keep trimming it back until the flesh is green with no signs of rot. Allow the cut portion to callus over for about a week in a dry location. Then plant in loose soil. Do not water the cutting until roots have been formed.
Hope this helps,
Will

[curious physicist]

Thanks!

Just a few more questions. Are the brown threads in the cut part of the bottom cactus normal? Where should I store the bottom part till it calluses over? Will it ever grow again? The cactus is at least 5 years old, is that old for a cactus, how much longer can it live? And finally, what type of soil should I plant the top part?

Once again, Thanks!

[iann]

The brown lines are not normal. I don't know what they are on your plant, They look a bit like splinters, possibly dirt that was forced into the plant by your surgery. Usually you should be very wary of discolouration getting into the vascular system but it doesn't look like that.

[curious physicist]

Help! I let the bottom callus over, but it has started to rot. What can I do?

[greenknight]

Anything rotten you cut off back to tissue that's not discolored. Good idea after you cut to dust it with flowers of sulfur (which you can get at any drugstore) or some other fungicide.

[curious physicist]

The only fungicide I have is a liquid with an active ingredient of "Extract of Neem Oil". Is that an effective fungicide?

[greenknight]

Neem oil wouldn't be appropriate, you want the cut to dry and scab over - any oil would block evaporation. Better to use nothing, just put it in a warm, dry place so it dries quickly.

[curious physicist]

Thanks for your help everyone. I've taken your advice, and bought sulfur powder, but the cactus is still rotting. Since posting last I have cut the rotten parts off twice, and dusted it with sulfur powder, but after a couple of days it just starts to rot again, eating away the inside while leaving the skin intact.

Any advice would be appreciated a lot.

[jmoney]

I guess make sure that the blade or tool you are using is clean. Make sure that you are cutting off enough to get past where it is rotting. The cut surface should look green, like in the initial post. Also, make sure it stays dry. If it gets wet, this will almost surely cause it to begin rotting again. I'm not sure it will help the plant but maybe try unpotting it while it calluses. That last bit of advice is just my own personal thought. A more experienced person on the forum might have some better advice.