What's eating my lady finger cactus?

Lady Finger Cactus, like other Mammillaria, is most troubled by mealybugs, which nestle in the tubercle grooves and wool-like tufts at the apex. Root mealybugs are a stealthy secondary threat. Spider mites may appear in very dry air. Regular inspection between offsets and prompt alcohol treatment keeps colonies in check.

White woolly deposits between tubercles and at the crown; weakened or yellowing stems Swab all woolly areas with 70% isopropyl alcohol; repeat every 7–10 days; isolate from other cacti

Invisible underground colonies cause mysterious wilting and poor growth despite normal watering Unpot, wash roots, treat with diluted neem drench, repot in fresh dry cactus mix

Webbing at the apex and between offsets; pale, dusty appearance on stem Increase humidity, rinse stems carefully, apply insecticidal soap spray