What's eating my samaipatensis cactus?

Cleistocactus samaipatensis shares the typical Cleistocactus vulnerability to mealybugs sheltering in its spine-covered areoles. Root mealybugs are a secondary risk, particularly in humid or poorly draining conditions. Scale insects occasionally establish on the columnar stems. Good drainage, strong light, and monthly inspection are the core defenses for this houseplant cactus.

Waxy white tufts at areoles and growing tips; stunted or distorted new growth Dab each colony with alcohol on a cotton swab; spray the whole plant with diluted neem oil every two weeks

Plant fails to put on seasonal growth; white waxy insects coat root tips when the plant is unpotted Bare-root, wash thoroughly, soak in neem solution, dry completely before repotting in fresh cactus mix

Hard brownish discs on stem ribs; associated sooty mould from honeydew excretion Physically scrape off with a soft brush, wipe with alcohol, apply horticultural oil and repeat after two weeks