What's eating my euphorbia groenewaldii?

Euphorbia groenewaldii, a rare dwarf South African succulent Euphorbia grown by collectors as a houseplant, is most threatened by mealybugs nestling in its tightly packed ribs. Scale insects and root mealybugs also pose risks. The latex deters most chewing insects, but sap-feeders readily exploit this slow-growing plant.

White waxy fluff in rib channels; honeydew secretion attracts sooty mould and slows growth. Apply 70% isopropyl alcohol via a fine cotton swab; follow with neem oil or insecticidal soap; repeat every 10 days.

Small hard or wax-coated bumps on the ribs; localised colour loss and sap depletion. Scrape off individually with a soft toothbrush or fingernail; apply horticultural oil; monitor and repeat fortnightly.

Plant stalls or deflates even with proper care; white powdery coating found on roots at repotting. Unpot, rinse and inspect roots, drench with dilute systemic insecticide, dry roots, and repot in sterile gritty mix.