Hey there. I recently purchased this barrel cactus from a shop in Denver and then took it with me back to NYC. (As carry-on.) It looks basically healthy except for this discoloration, which seems to come in two parts. At the upper end of the plant there are these lighter (yellowish) spots. With an x-acto knife I can slice them off, tho it’s not the easiest thing in the world to do. Towards the bottom, the discoloration isn’t raised, and it’s pretty thorough at the bottom two inches, creeping up in some places.
Maybe the bottom is natural barking, and the top is related to frost in Denver? In which case, let it be?
Or maybe it’s a scale infestation? In which case, should I take that knife to everything I can?
Spent forever online looking for advice but have gotten nowhere. Any thoughts you have would be so appreciated!
It’s hard to tell from the photo. It’s either some previous damage that has healed over, in which case you don’t need to do anything. Or it’s scale, which is an insect, so please put away the exacto blades. If you think it’s scale then you should spray it with an organic insecticide. You can also dip a soft paintbrush into rubbing alcohol and that will break the shell down so that you can clean them off after they are dead.