Scale Insects on Houseplants
Scale insects are armored or soft-bodied sucking pests that attach to stems and leaves and feed on plant sap. Adults look like small brown or tan bumps and don’t move once settled. Heavy infestations weaken the plant and produce honeydew that attracts sooty mold.
How to identify scale insects
Small (1–5 mm), oval to round, brown or tan bumps on stems, petioles, and leaf undersides. They don’t move and can be scraped off with a fingernail. Sticky honeydew below the plant is often the first clue.
Damage to look for
Yellowing leaves, leaf drop, slowed growth, sticky honeydew, sooty mold on lower leaves.
Life cycle (why they spread so fast)
Crawlers (mobile young) hatch from under adult scales and move to new feeding sites before molting into the immobile adult stage. Indoors there can be 2–3 overlapping generations a year.
How to get rid of scale insects
- Scrape visible adults off with a fingernail or soft toothbrush, then wipe the area with a cotton swab dipped in 70% isopropyl alcohol.
- Spray the whole plant with horticultural oil (1–2%) or insecticidal soap, repeat every 10–14 days for 3–4 cycles to catch crawlers.
- Systemic imidacloprid drenches (per label, not on edibles) work for stubborn infestations on woody indoor plants.
- Isolate the plant for 6–8 weeks after the last visible scale.
How to prevent scale insects
- Inspect new plants closely along stems and the underside of older leaves.
- Wipe leaves and check stems monthly.
- Quarantine new plants for 3–4 weeks.
Per-species treatment guides
Treatment varies slightly by plant. Find your species below for a dedicated guide.
Source: UC IPM — Scales