What's eating my euphorbia columnaris?

Euphorbia columnaris, a rare columnar succulent Euphorbia from Somalia kept as a collector's houseplant, faces its greatest indoor threat from mealybugs in rib channels and scale insects on its columnar body. Spider mites occur in low humidity. The poisonous latex strongly deters chewing pests and browsing animals.

White fluffy wax in rib grooves and near the growing tip; stunting and honeydew accumulation. Remove with an alcohol cotton swab; apply neem oil or pyrethrin spray to the full plant surface; repeat fortnightly.

Flat or convex waxy bumps along the column; localised yellowing and surface scarring. Dislodge scales with a soft brush dipped in soapy water; apply horticultural oil; monitor weekly and repeat as needed.

Pale stippling across the columnar surface; fine silken webbing in very dry air. Rinse carefully with tepid water, apply a miticide or dilute neem oil, and maintain slightly higher humidity.