Question
It is now winter here in tasmania, australia. Pretty wet and cold. I noticed orange/rust coloured markings on my m.madisoirum..I thought it was rot, cut the surface, but found no rot. Today I noticed that a prickly pear had this orange mark, i cut in and found rot extending a great deal into plant. I cut out. How do I deal with this problem, as I hear some plants can be entirely turned to mush by this rot. Will it spread to my other cacti?

Answer
Chris,

I am not too familiar with that type of rot, but I did find some thing that might help. Please read an article at this web page: http://www.labs.agilent.com/botany/cacti_etc/html/soils.html  , especially from the paragraph that starts "I live in Albuquerque, NM". It is more than likely the moist atmosphere that is the culprit. Hopefully this helps.

Sincerely,

Greg