I have a ruby ball moon cactus that I have only had for a few months...I
noticed some purple patches and found online that it was most likely
sunburn so I moved the cactus to keep it out of the direct sunlight. Today
I noticed that almost half of the red ball is black and almost looks like
rot...I am wanting to cut the red ball completely off and just let the
bottom part grow as it would have before grafting. I really need to know
how to sterilize a blade and how to do it properly so that I don't kill
what is still salvageable...any suggestions?

~Katie