Vacation Cactus Suffers
Hello! I have had this cactus for about 7 years and a friend “babysat” it for me for about 1 1/2 years while I was traveling quite a bit. I just got him home and noticed several problem areas. After looking at your blog (which I totally love!) and other websites, I am still not sure if this is a fungus, a scale problem, a dreaded virus, old injuries or nothing to worry about! There are good shots of the problem areas. Thank you so much for taking a look.
It looks like the spots are barked-over, healed infections of some kind. You could spray them with Neem Oil just to be on the safe side, but it does look like the plant has fought off the infection and is doing fine. If more start then the infection is back and you should treat with Neem Oil which is a natural fungicide that usually is effective without being too dangerous to use on a houseplant. I like the Greenlight Organic Neem Oil, which you should be able to find at local nursery or garden center. If it is a virus there is not a lot you can do but seaweed extract seems to help boost plants immunities, so you can give a few douses this fall and then again next spring. But do not fertilize this late in the year, since the plant is about to go dormant for the winter.