White Cottony Patches on Houseplants: Check for Mealybugs
White fluff on a stem may be mealybugs, but dust, mineral deposits and natural plant hairs can look confusingly similar. Look for the organism, not just the color. Separate a suspicious plant before brushing material onto nearby foliage.
Inspect the sheltered places
Use good light and magnification to check leaf joints, undersides and stems. Mealybugs are soft-bodied insects with a waxy covering; some infest roots. Sticky honeydew can accompany feeding, but other sap-feeding insects also produce it. Photograph both a close view and the whole plant. A yellow leaf alone cannot identify the pest.
Match the response to the finding
If the white material is an unchanged natural covering, avoid scraping it away. If live mealybugs are confirmed, keep the plant separate and inspect neighbors. Small accessible colonies can sometimes be removed physically, but hidden insects may remain. Severe infestations may justify discarding the plant rather than repeatedly exposing the collection. Bag it before moving it through other plants.
Choose treatment deliberately
UC IPM describes alcohol spot treatment with a warning to test plant sensitivity first. Do not turn that into a whole-plant homemade spray recipe. If using a pesticide, its local label must permit the pest, plant and indoor use; follow its dilution, precautions and repeat instructions. Household cleaners are not interchangeable with labeled insecticidal soap. (UC IPM)
Monitor fresh activity
Record locations of colonies, the action and subsequent live insects under comparable inspections. Old wax or dead insects are not the same as a new colony. Repeat inspection of leaf joints and nearby plants; a clean-looking surface immediately after wiping does not prove eradication. If identification remains uncertain, seek horticultural help with clear photographs before adding treatments.