Question
Hello I have a cactus that I bought a year ago that has developed a white substance in small blobs on the surface. I don't know what this is, could you tell me whether this is normal or not and if I have done something wrong for this to develop. I have not had any cactus plants before this.Thanks alot for your help.

Answer
It sounds like you may have mealy bugs.  If there aren't a ton of the white cotton like areas, take a cue tip and take the stuff with alcohol.  If there are, get a a combination insecticide and fungicide and treat it with that.  That should take care of them.  You didn't do anything wrong.  Cacti are susceptible to mealies.  Water sparingly and if it's been in the same pot for a year you might want to repot when the mealies are gone.

Maureen