help, black spot on one of my babies

[daffe]

Hi, what is this on my Bolivian Torch Cactus? Its a black spot and it seems like its under the skin. Its only on one of them.

[jmoney]

The photo is kind of blurry so it is hard to see. Looks like rot to me. I'm not sure what you can do to save it. Cut that little portion off? I wouldn't do anything drastic until hearing from others.

[daffe]

[jmoney]

Definitely looks like rot to me. Again, wait for some additional opinions though.

[greenknight]

I think surgery is called for.

[daffe]

if it is rot, is it from to much water? to low temperature or what?

[daffe]

I think surgery is called for.

cut it off? I see some recomend sulfur powder, should i put some sulfur powder on the black spot?

[jmoney]

You may have to cut that small portion out. I think sulfur powder is used after cutting it out?

[HP22B]

If you're going to cut it make sure your knife is fully disinfected first. I've had similar black spots like this on similar cacti that turned out to be damage from either snails or punctures that eventually turned white like corking. They always started out pale black however.

[daffe]

If you're going to cut

So i dont need to cut?

[HP22B]

I'm no expert but I'd say cut if it's soft and spreading, leave it be if not.

[daffe]

ok, it dont look like its spreading, but its hard to tell if it is soft or hard on a litle spot. I will wait some days and look. Is it only puncture on the skin that make rot?

[hegar]

It looks like some kind of organism made an entrance near the areole that shows the dark discoloration. What is worrisome to me is the chlorosis that seems to be present from below said areole, all the way through the whole stem, including the top of the plant.
The safest thing to do would be to cut the stem off with a disinfected knife to the level of the lower areoles. Of course, this can be a "risky operation", especially if the plant is very small. If the discolored tissue, including the area taken up by the lighter green color increases, it would most likely kill your plant quickly.
So, surgery may be the only way to save it. However, you may lose it, no matter what you decide to do.

Harald

[daffe]

ok, but could it spread to the other cacti in the same pot?

[greenknight]

Yes, it could spread to the others, but you greatly reduce the chance of that if you remove the rot before it produces spores. Good idea to dust the others in that pot with sulfur, too. It just takes a very light dusting.

I second everything Harald said, he summed it up very well.