I have had my ruby ball cacti for....at least 4 years. The red flower on top dried up forever ago, but stem has been green and healthy. Not too long after I bought it, it started growing a growth on one of the top corners of the stem. It has been growing longer over the years and offers no harm, I even built a little stand to hold it up. (Im not sure if it's normal, I was thinking maybe it happened because of the plant food I gave it when I first got it but idk). Anyways, I noticed today that the main stem is not the healthy green anymore and is now yellowy and sickly. The growth is still green and healthy looking though. I really hope it's not dying and there's something I can do to help:( I replaced the soil already, and I haven't changed its position. It's been on the same window seal as long as I've had it. Any ideas on whats wrong and what else I can do to revive its health? Thanks.
The red part was the ruby ball, a red color variant of a cactus plant. It was grafted onto a Cereus cactus, which grew its own new stem off to the side. It might be C. undatus, (Hylocereus undatus), night-blooming cereus, Honolulu queen etc. Look up how to grow that.
The grafting stock in this case is a Hylocereus, and the main stem i dead. The disease will spread to the offset too, but if you hurry you can cut off the green parts and try to root them if you want. If the tissue is discoloured (orange/red/brown/black) it is infected and cannot be saved (even if the skin is still green on that part).
