What's eating my fire barrel cactus?

Fire Barrel Cactus (Ferocactus stainesii) is a large Mexican barrel cactus with red spines, grown as a houseplant or patio statement plant. Scale insects are the commonest pest on large Ferocactus, clustering on ribs. Mealybugs hide in spine axils. Spider mites attack in low humidity. Heavy spination makes treatment challenging — use long tools and gloves.

Hard round bumps along ribs, especially near spine clusters; yellowing tissue; sooty mold on honeydew. Brush off with a stiff alcohol-dipped brush while wearing thick gloves; follow with neem oil spray along all ribs; repeat every two weeks.

Woolly white deposits in spine axils and rib grooves; slow growth; sticky residue. Apply isopropyl alcohol carefully with a cotton swab; spray with insecticidal soap or neem oil; repeat weekly until clear.

Silky webbing between spines; bronze or dull patches on the stem surface; worst in dry heated rooms. Mist the stem lightly; apply neem oil or a miticide spray; move away from dry heat sources and improve ventilation.