Scale insects are small, flat or domed bumps that stick to stems and leaves and do not move. To get rid of them, isolate the plant, scrape or wipe off every bump, spray the whole plant with insecticidal soap or horticultural oil, and repeat every week for at least a month.
Scale is harder to kill than mealybugs or spider mites. The adults sit under a hard or waxy shell, and that shell blocks most sprays. Sprays work on the young. Your hands and a cotton swab work on the adults. You need both.
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How to know it is scale
Scale looks like a plant problem, not a bug. Most people see brown bumps and think they are part of the stem.
Look for these signs:
- Round or oval bumps, tan, brown, or black, about 1 to 4 mm across
- Bumps along the stem, on leaf undersides, and beside the main vein
- Bumps that never move
- Sticky leaves or a sticky surface under the plant
- Yellow leaves, weak new growth, or leaf drop on a plant that was fine before
The stickiness is honeydew. Soft scale insects make it. Armored scale does not. A plant with armored scale can have no sticky residue at all, so a clean leaf does not rule out scale.
The fingernail test
Scrape one bump with a fingernail. A scale insect pops off the stem. It may leave a small pale mark or a wet smear. A natural part of the plant stays put.
Live scale is plump and may squish. Dead scale is dry, flat, or hollow. The shell stays stuck to the plant after the insect dies, so a dead bump looks the same from a distance. Check by flipping it off. Count only the live ones when you decide if the plant is clear.
What it might be instead
Two things get mistaken for scale.
- Edema. Overwatered plants can grow small corky or blister-like bumps on leaf undersides. They are part of the leaf. They do not scrape off as a shell. If the plant has been sitting in wet soil, read how to tell if a houseplant is overwatered or underwater.
- Mealybugs. These are soft, white, and fluffy. Scale is smooth and hard. The plan for mealybugs is close to this one. See how to get rid of mealybugs on houseplants if the bumps are white and cottony.
Step 1: isolate the plant
Move the plant away from every other plant. Young scale, called crawlers, walk to nearby plants. They are the only stage that moves.
Check the plants that stood close. Look at stems and leaf undersides. Wipe the shelf where the infected plant sat with soapy water.
Step 2: remove every bump you can reach
This step does the most work. Adults under their shells survive most sprays, so take them off by hand.
- Dip a cotton swab in 70% isopropyl alcohol. A bottle of 70% isopropyl alcohol from Amazon and a box of swabs are enough.
- Test one leaf first. Wait 24 hours. Thin or waxy leaves can burn.
- Rub each bump with the swab until it loosens. Use a soft toothbrush or a fingernail on stubborn ones.
- Wipe the spot clean with a damp cloth.
- Work along every stem, then the underside of every leaf.
Cut off stems or leaves that are covered. Bag them and put them in the trash. Do not compost them. A plant looks worse for a while after heavy pruning, but new growth will come back clean.
Step 3: spray the whole plant
Spray to catch the crawlers and any bump you missed. Insecticidal soap kills soft-bodied young scale on contact. Horticultural oil and neem oil smother them. A ready-to-use insecticidal soap spray from Amazon is the simplest choice.
Follow the label. Cover the tops and undersides of leaves and all of the stems until the plant is wet. Spray out of direct sun, since wet leaves in strong sun can burn.
Oils can harm some plants. Ferns, palms, and plants with fuzzy or very thin leaves can react. Test one leaf and wait a day before you spray the whole plant.
Skip homemade dish soap mixes. A strong mix strips the leaf coating.
Step 4: repeat every week
Scale eggs and crawlers keep appearing for weeks. One round never clears a plant.
Wipe and spray every 7 days. Keep going for at least four weeks. Many plants need six to eight. Stop only after you check twice in a row and find no live bumps. Use good light and look at every stem.
Rinsing the plant in the shower between rounds washes off honeydew and loose crawlers. Use lukewarm water. Let the pot drain before it goes back.
Step 5: clean up the honeydew
Sticky leaves attract sooty mold, which is a black film. The mold does not hurt the plant directly. It blocks light. Wipe leaves with a damp cloth and a drop of mild soap. The mold comes off once the scale is gone.
Plants that get scale most
Scale shows up on many houseplants. Common targets include fiddle leaf fig, rubber plant, citrus, schefflera, jade plant, palms, ferns, orchids, hoya, and sago palm. Plants with thick stems and woody growth give scale many places to sit.
Check these plants each time you water. Look at the stem and the undersides of the older leaves first.
How scale gets in
Scale usually comes in on a new plant or on a plant that spent summer outside. Look over every plant you buy before it goes near your others. Keep it apart for two to four weeks. The same rule applies to plants that come back indoors in fall. See how to bring houseplants inside for winter without bugs for a full check.
When to let a plant go
A plant covered in scale from the base to the tips, with most stems already weak, may not be worth saving. If you want to try, cut it back hard and treat what is left. If the plant is a cutting-friendly type, take a clean cutting from the newest growth, check it closely, and start over. Throw out the old soil and wash the pot in hot, soapy water before you reuse it.