Question
Hi - I have/had a beautiful columner cactus that has grown a foot since I
purchased it. My house was sprayed for bedbugs and apparently, the
exterminator sprayed the cactus. The bottom 12" is all dried out and today
the top fell  over (it's still connected to the dead part). The top 2 + feet are
still green and healthy looking. Is there anything I can do?
Thank you so much.  

Answer
Hello Lara,
Cut off all leafs (or columns for some cacti) and root them using the instructions given on my website below. I can't guarantee you the base will survive, but give it shot. Remove the plant from the pot and soil. Leave it so it is bare plant and roots. Wash the roots thoroughly with fresh water 10% bleach. Wash the base too as much as possible just in case it has poison left on it. Then wash it again with plain freshwater. Cut off any rotting or infected roots to prevent it from spreading. Then plant it in new, clean cactus soil with a new pot. Be sure to fill in the gaps between the roots when putting the soil in. If successful, the plant will continue to grow without dying. It might shoot new buds if really successful.

http://www.cactaceae.t83.net/#/propagation/4532016273