Potential Bacterial Infection

This is a very unusual example. We believe it to be a bacterial infection however they are usually not seen in a perfect bad around the plant. The top looks remarkably healthy so there are 2 things to consider. When did this show up? If it was a long time ago say a year, then I wouldn’t worry about it as it appears to have overcome the problem. If it has just shown up somewhat recently then you need to take some drastic measures. That would be severing the healthy part from the diseased part. Start by cutting straight through about 3″ above the black area. If the cut on the top piece looks nice and white / green and no signs of brown, then you have a healthy cutting. If you are still seeing some discoloring, cut off another inch. You can repeat this as necessary until you hit healthy tissue, and sterilize the knife between cuts. Dust the healthy cut surface heavily with ground cinnamon, it is a natural antibacterial. Let your new healthy cutting sit somewhere cool and out of the sun for about 10 days. Then plant it in a new pot that’s not too big with new cactus soil, and do not water it for another 10 days. Then you can give it a thorough watering and do not water again until the soil has become nearly dry. All of the parts of the old plant should be disposed of including the soil and the pot – You could sterilize the pot by soaking it in a 10% bleach and water solution so that you can reuse it for something else. It is way too big to use for the new cutting.