Im hoping you can help.
I bought this cactus from you a few years ago. It doesnt seem to be doing very well….
What can I do to help it!
It looks like it has caught an infection. It could be fungal or viral… it is hard to tell from the photos. The best treatment I can suggest is Neem Oil, which is a natural fungicide that you can spray on as well as douse the soil with. Spray the entire plant until coated and then retreat in a week to ten days. If two treatments stop the spread it is fungal, if not it is likely a virus and there are not any treatments that are “over the counter” for use. The option then is to feed the plant with Kelp and a low strength fertilizer to boost the plant’s defenses and then keep it warm and dry for the winter and hope it can fight it off.
If you want to bring it by the nursery we would be happy to look it over and see if we can give better advice in person. If you are not close to Berkeley Neem Oil should be available at any good nursery, we prefer the 100% or organic versions since some of the products marketed for use on roses have a solvent added that is rough on cacti and succulents when applied in full sun.