Anybody ever seen this before? I've been growing cacti for about 15 years and have never seen this. Lost a large portion of my collection last year to it. It starts at the bottom and moves up over a period of 1-2 months. The only way I have found to save the plant is to top it and re-root. Sometimes even that doesn't work. The only thing I can think of is that last year I put most of my plants on top of wooden planks to keep the snails away. Maybe some fungus in the wood made it way into the soil and roots.