What's eating my twisted barrel cactus?

Twisted Barrel Cactus (Ferocactus herrerae) is a large, heavily spined houseplant most threatened by root mealybugs, which can destroy the root system before symptoms show above ground. Cochineal scale and spider mites are common surface pests. Because of its imposing spines, use long-handled tools and heavy gloves whenever treating this plant.

White waxy clusters on roots; plant body shrivels and fails to recover after watering; crown softens in late stages. Unpot carefully (thick gloves required), strip all compost, rinse roots, soak in diluted neem oil, and repot in fresh, sterile cactus grit.

White cottony deposits visible between ribs and around areoles; red dye released when touched; plant body turns yellow. Use a long-handled soft brush soaked in isopropyl alcohol to treat deposits; follow with neem oil or insecticidal soap spray every 10 days.

Very fine pale or rusty stippling across the cactus ribs; webbing in dry, warm spells. Increase air circulation, apply insecticidal soap or neem oil with a syringe or pump sprayer, and repeat weekly for three treatments.