HELP!!! What are these Orange sploches on my M.F?

Hey all, I am somewhat new to cacti. We just moved to AZ so I thought I should give some new varieties (to me) a try. So I totaly fell in love with those big Mexican fence post cactus and bought a few smaller ones. After a few weeks I repoted them into thier new home, a 10"/12" pot and found a spot outside that gets direct sun for about 5/6 hours a day. They did ok for a few months. Then yesterday I went out to check on them because we had a few days of rain & lower temps. I was horrified to find these wierd orange splotches over a few of them. My guess is it's some kind of fungle shmutzs. I promptly dragged the pot inside, put a grow light on it and left it be. What I need to know from all the cactus kings and queens out there are the following:

1. am I correct in thinking this is a fungus?
2. Is it safe to put a fungicide on it if it is a fungus.
3. If it isn't a fungus what is it & how do I treat it.
4. any other helpful advice you can offer. Thanks in advance!