White cottony tufts in leaf joints are mealybugs; small brown or tan bumps on stems and leaf veins are scale; both leave sticky honeydew on leaves and furniture. Isolate the plant, wipe or dab every visible insect with a cotton swab dipped in 70 percent isopropyl alcohol, then spray insecticidal soap or horticultural oil every 5 to 7 days for at least four weeks, because eggs and young crawlers keep hatching.
How to identify them
Both pests suck sap and weaken plants slowly, which is why they often go unnoticed until a plant looks tired and sticky.
| Sign | Mealybugs | Scale |
|---|---|---|
| Look | White, cottony, oval, slow-moving | Brown, tan, or white bumps that do not move |
| Where | Leaf joints, undersides, new growth, roots | Stems, leaf veins, leaf undersides |
| Clue | Waxy white fluff | Bumps scrape off with a fingernail |
| Both | Sticky honeydew, black sooty mold, yellowing leaves | Same |
Check new plants, plants that summered outdoors, and anything brought inside for winter. Use a magnifier and look at the joints where leaves meet stems.
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Find My Plants →Step 1: isolate and clean up
Move the plant away from others right away; crawlers travel on touching leaves. Prune off heavily infested stems and bag them. Rinse the plant in the shower or sink with lukewarm water to wash off honeydew and loose insects, covering the soil to keep it in the pot.
Step 2: spot treat with alcohol
Dip a cotton swab in 70 percent isopropyl alcohol and touch each mealybug; it dissolves their waxy coat. For scale, rub the bumps off with the swab or a fingernail. Test on one leaf first and wait a day, since a few thin-leaved plants show spotting.
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Step 3: spray on a schedule
Spot treatment misses eggs and tiny crawlers. Follow up with insecticidal soap or a horticultural oil labeled for houseplants.
- Spray leaf tops, undersides, stems, and leaf joints until wet.
- Repeat every 5 to 7 days for at least four weeks.
- Keep plants out of direct hot sun and away from heaters for a day after oil sprays to avoid leaf burn.
- Wipe off dead scale shells; they stay attached after the insect dies.
Check the roots too. Root mealybugs look like white powder on the root ball. If you find them, remove old soil, rinse roots, and repot into fresh mix and a clean pot.
Why they keep coming back
Mealybugs and scale return when a few eggs or crawlers survive in a hidden spot: under a leaf sheath, in the pot rim, or on a neighboring plant. Wipe down the pot, saucer, and nearby shelf, and check every plant that shared the windowsill. Keep the infested plant isolated until two weekly checks in a row show nothing new. Sticky honeydew on a table or floor is often the first sign of a repeat, so look up when you find it.
When to give up on a plant
A small plant covered from top to bottom is often better discarded than treated, to protect the rest of your collection. Large or treasured plants can be cut back hard and treated.
Prevention
- Quarantine new plants for two to three weeks. See our guide to gift plant acclimation after purchase.
- Inspect plants coming in from outdoors; citrus, jade, succulents, and ferns are common hosts. Our guide to moving citrus and tropicals indoors covers the checks.
- Avoid overfeeding with high-nitrogen fertilizer, which produces soft growth that sap feeders favor.
Safety and pets
Follow product labels for rates and plant types. Keep pets away from sprayed plants until the leaves are dry, store alcohol and sprays out of reach, and ventilate the room when spraying. Many common houseplants are themselves toxic to cats and dogs if chewed, so check the specific plant with the ASPCA list or your veterinarian rather than assuming a plant is harmless. For edible herbs, use a product labeled for food crops and follow its harvest interval.
Bottom line
Isolate, rinse, dab with 70 percent alcohol, then spray soap or oil every 5 to 7 days for a month, and check the roots. For other winter pests, read spider mites on houseplants in dry heat and fungus gnats in houseplants.
Related reading
- Humidity trays and grouping for winter houseplants
- Soil moisture meters for houseplants
- Grow light basics for winter houseplants
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