What's eating my blue torch cactus?

Blue Torch Cactus (Pilosocereus pachycladus) is a tall, vivid-blue columnar houseplant. Its waxy blue coating (pruinose) can mask early pest damage. Mealybugs and scale insects are the most common indoor threats, exploiting the areoles and rib grooves. Spider mites strike in hot, low-humidity rooms. Root mealybugs can also affect plants kept too moist in winter.

White cottony wax at areoles and rib grooves; affected stem sections lose their vivid blue coating and turn pale. Dab colonies with 70% isopropyl alcohol; spray the full plant with neem oil weekly for 3–4 weeks.

Hard brown bumps adhering to the blue stem; honeydew drips down the column and sooty mold may follow. Remove with a soft brush and rubbing alcohol; apply insecticidal soap every 10 days until all scales are gone.

Fine silky webbing between spines and faint bronzing of the blue stem surface in dry heated rooms. Move to a more humid location; wipe stem with a slightly damp cloth and apply diluted neem oil spray weekly.

White powdery colonies on the roots; plant wilts or fails to grow despite adequate light and occasional watering. Unpot and inspect roots; wash off all soil, let roots dry, and repot in fresh well-draining gritty compost.