What's eating my cleistocactus hyalacanthus?

Cleistocactus hyalacanthus, a columnar cactus with fine glassy spines grown indoors, is most commonly troubled by mealybugs hiding at its areoles and scale insects clinging to the stem. Spider mites can colonize the tip in dry centrally-heated rooms. Root mealybugs are possible if the substrate stays damp too long.

Cottony white deposits accumulate at spine clusters along the column; plant growth slows and stem may discolor. Dab with rubbing alcohol; spray with neem oil or insecticidal soap and repeat every 10–14 days.

Hard or soft brown bumps attach along stem ribs; honeydew secretion encourages sooty mold. Scrape off physically, then treat with horticultural oil or systemic insecticide containing imidacloprid.

Fine pale stippling near the growing tip; invisible webs between spines in severe cases. Increase humidity around the plant; spray with diluted neem oil solution weekly until symptoms clear.