I have a euphorbia ammak that I left with a friend for a couple weeks while I was out, and when I returned I noticed a brown spot at its base. It looks like rot and there are little pustules in the area, but it's not soft, it's as hard as the rest of the cactus. Is this definitely rot? If it is, I ...

I have a euphorbia ammak that I left with a friend for a couple weeks while I was out, and when I returned I noticed a brown spot at its base. It looks like rot and there are little pustules in the area, but it's not soft, it's as hard as the rest of the cactus. Is this definitely rot? If it is, I k...