What's eating my oreocereus trollii?

Oreocereus trollii (Old Man of the Andes) is mainly troubled indoors by mealybugs hiding in its dense white hair, and by root mealybugs or root rot from overwatering. Spider mites can colonise in hot, dry conditions. Its woolly coat makes early detection difficult — inspect the base and spine clusters regularly.

White waxy cottony clusters lodged in the woolly hair and between areoles; sticky honeydew; stunted growth Dab individual bugs with a cotton swab dipped in 70% isopropyl alcohol; for heavy infestations spray with neem oil solution; repeat every 7–10 days

Unexplained wilting, yellowing, and poor growth despite correct watering; white waxy powder visible on roots when unpotted Unpot, shake off soil, soak roots in a systemic insecticide solution (imidacloprid), allow to dry and repot into fresh, sterile cactus mix

Fine webbing between spines and areoles; stippled or bronzed skin; overall dullness Increase humidity slightly and rinse with a forceful water spray; apply insecticidal soap or neem oil; repeat weekly for 3–4 weeks