Question
I have a 10 year old cactus, tall, no arms or legs...just tall with little stickers. I have basically just let it grow and have left it alone. It became at least two feet high growing straight up. Life is good then all of a sudden the top of the the cactus started to turn black. About three inches is black. Not knowing anything about cactus's I transplanted it hoping it would help. It is still black on top. Should I cut it off ..suggestions?

Answer
It sounds like rot, Jill.  The only way to get rid of it is to cut it off.  Take a sterilized knife, very sharp and cut at least 1-2 in. below the rot.  I there is still black, resterilize your knife (with ETOH) and cut further .  Repeat until you see healthy, green, white tissue.  I'd brush that with a fungicide ore rooting powder.

If the roots looked white and healthy when you transplanted and you planted in well draining soil, the plant should do OK.  Keep in mind that it will be disfigured. Not knowing what kind of cactus you have I don't know if it will develop off shoots.  If has been 10 years, I doubt it will.  Some of the columnar cacti don't.

Be sure to dispose of all the rotted tissue and don't compost it.

good luck,

Maureen