What's eating my silver torch cactus?

Cleistocactus strausii is covered in dense white hair-like spines that give excellent camouflage to mealybugs — the most common pest. Scale can attach beneath the spine coat undetected. Root mealybugs exploit the clustered columnar habit. Routine inspection by gently parting the spines at the base and upper areoles is essential for early control.

Cottony white colonies blending into the white spines; yellowing or soft tissue beneath affected areoles Part spines with tweezers and apply 70% isopropyl alcohol with a fine brush to each colony; treat monthly

Columns do not elongate seasonally; powdery white insects visible on roots at repotting Lift and bare-root all columns; soak roots in diluted neem, air-dry fully, repot in fresh porous mix

Tan or brown fixed bumps under the spine cover on ribs; honeydew accumulates at base Remove manually with a soft brush and alcohol wipe; treat with horticultural oil; repeat in 14 days