Question
old man cactus
Hi, we have a fairly large old man cactus and noticed a black soft spot toward the top. The spot seems to have gotten bigger and it is only in this place. Want to save the cactus if possible.
AnswerDear John,
Unfortunately that is black rot. Usually when you see it it's even more extensive inside the plant. The only way to save the plant is to get rid of all of it. So... get a very sharp knife and sterilize it with alcohol. Scoop out the rot until you get to clean tissue, white/green with no discoloration AT ALL. Sterilize the knife with each new cut. If you get rid of all of it brush it with a fungicide. It will leave a hole that won't fill in, it will just callous over.
Sometimes that treatment is successful. If there isn't enough healthy tissue left the only thing you can do is slice it off below the rot, again to clean tissue, then you'll have a flat topped
cactus. Either way, if you do save the plant you'll need to repot it and throw the old soil away.
You're not going to know what you're dealing with till you dig in.
Good luck,
Maureen
