Pest
Scale Insects
Brown raised bumps on stems and leaves, insect visible when pried open
Overview
Scale insects are among the most stubborn houseplant pests. Adults are covered by a waxy scale covering (circular or oval, 1-5mm diameter) that looks like tiny barnacles attached to stems and leaves. The scale protects the insect, making standard contact insecticides ineffective. Scale insects use piercing-sucking mouthparts to feed on plant sap, excreting large amounts of honeydew that promotes sooty mold.
Symptoms
Brown, gray, or white circular/oval hard bumps adhere to stems and leaf veins, difficult to peel off. Prying open the scale reveals bright orange-yellow or red soft-bodied insects underneath. Sticky honeydew coats leaves; severe cases develop black sooty mold on the honeydew. The plant weakens, leaves lose luster, and new shoot growth stalls.
Treatment
For light infestations: dab each scale with an alcohol-soaked cotton swab — alcohol dissolves the waxy coating and kills the insect beneath. Alternatively, pick them off with a toothpick or tweezers. For moderate infestations: spray with horticultural oil (narrow-range oil, Neem oil), which suffocates scale insects by blocking their breathing pores. For severe cases: apply systemic insecticide (thiamethoxam) as a soil drench every 10 days for 2 treatments.
Prevention
Regularly inspect leaf axils, stem nodes, and leaf undersides — scale insects' preferred hiding spots. Thoroughly examine new plants before introducing them. Maintain good ventilation and light. If ants appear, check for scale insects.
