What's eating my saguaro cactus?

Saguaro Cactus (Carnegiea gigantea) is a slow-growing iconic desert cactus kept as a houseplant when young. Mealybugs and scale insects are the main indoor pests. Root mealybugs can stunt already slow growth imperceptibly. Spider mites attack in low-humidity indoor conditions. Young plants are far more vulnerable than mature specimens — inspect every few weeks.

White fluffy deposits between ribs and at the growing tip; slowed growth and honeydew residue Dab with 70% isopropyl alcohol swabs; spray with diluted neem oil or insecticidal soap; repeat every 7 days for a month

Hard brown or grey bumps fixed to the rib skin; yellow halos around feeding sites Scrape off manually with a soft brush; apply neem oil spray; use systemic insecticide for widespread infestations

White waxy residue on roots; extremely slow or zero growth even with correct care Carefully unpot, inspect roots, wash and dry, then repot in fresh gritty sterile mix; water with systemic solution if infestation confirmed

Fine webbing along ribs; dull, slightly rough skin texture on an otherwise smooth young column Rinse plant, increase humidity slightly, and spray with neem oil or a miticide; repeat every 5–7 days