How to get rid of mealybugs

Almost always from a new plant. Mealybugs are common in nurseries, and the crawlers are small enough to miss. They do not appear out of nowhere and do not fly in. Once inside, crawlers walk across touching leaves and pots to the next plant.

Indoors all stages are present all year, so an infestation never pauses for winter. Old plants that never fully got clean are a classic source for the rest of the collection.

The plants they favour: succulents and cacti (jade, echeveria, string of pearls, Christmas cactus), hoya, orchids, African violets, ponytail palm, croton, schefflera, ficus, dracaena and citrus.

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   Step 1. Separate the plant. Move it away from the others, including from leaves it touched.

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   Step 2. Dab off every tuft. Dip a cotton swab in rubbing alcohol (isopropyl, 70 % or weaker) and dab each tuft and egg sac. The alcohol dissolves the wax and the insect comes off on the swab. Use a fresh swab for each round. Some leaves mark where alcohol touches them, so test one leaf a day or two before.

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   Step 3. Rinse the plant. Shower it with lukewarm water aimed into the leaf joints and undersides. That removes the ones you missed and the sticky film. Cut out tips covered in tufts.

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   Step 4. Treat a larger infestation carefully. UC IPM describes a 10 to 25% isopropyl alcohol solution in water as a spray option. Test a small area one or two days beforehand, target the mealybugs and avoid direct sun or plants stressed by lack of water. Do not add household soap. For an insecticidal soap, follow a label covering the plant, mealybugs and indoor use.

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   Step 5. Or a horticultural or neem oil. Oils smother mealybugs under a film. They need the same direct contact and can mark hairy or waxy leaves, so test first.

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   Step 6. Mealybug destroyers and parasitic wasps. The ladybird Cryptolaemus montrouzieri, sold as "mealybug destroyer", eats mealybugs and their eggs. Release it when there are many egg sacs, because its young need them, at above about 20 °C (68 °F) and 50 % humidity. Parasitic wasps (Leptomastix and relatives) attack specific mealybug species above about 15 to 18 °C (59⁠–⁠64 °F), so the species needs to be known. Both suit a group of plants or a conservatory better than one pot, and need several weeks without spraying.

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   Step 7. A systemic product, with care. Systemic houseplant products are watered in or pushed in as spikes, and the plant takes them up. They are less reliable against mealybugs than against other sap suckers, and they can harm pollinators, so avoid them on plants in flower and use them only when hand removal and sprays have failed. Use only a product whose label names houseplants and mealybugs.

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   Step 8. Check back every three to four days. Leaf joints, stalks, growing tips, leaf undersides, under the pot rim and the outside of the pot. Dab off anything new the same day. The plant goes back only after two checks in a row with nothing found. Wipe the spot it stood in.

A related kind lives on the roots. If a plant is struggling and barely growing while you find nothing on the leaves, take it out of the pot and look at the root ball.

White cottony deposits on the roots and on the inside wall of the pot are the sign. They look like mold but sit on the root network itself.

In that case, wash the mix off the roots completely and set the plant into fresh substrate in a cleaned or new pot. The old mix goes in the trash rather than back into another pot.

Check that plant’s root ball again over the next months while you water. A remnant left in the mix rebuilds the population slowly.

Root mealybugs are noticed most often on African violets and other small potted plants, and usually only when the plant is taken out of its pot.

Rubbing alcohol on a swab is the home remedy that works best. Diluted to 10 to 25 % it also works as a spray.

Dawn and other dish soaps are detergents. They can kill mealybugs they reach, but their additives can burn leaves. Insecticidal soap is made for this.

Masking tape pressed on and peeled off lifts crawlers and loose wax from tough leaves. It is a helper, not a treatment.

Vinegar burns leaves faster than it kills mealybugs under their wax.

Neem oil works by contact and needs repeat rounds.

Cold showers alone remove some insects and leave the egg sacs. Combine rinsing with swabbing.

Expect four to eight weeks. Each female lays 100 to 200 or more eggs over two to three weeks, eggs in the wax sacs survive any single treatment, and indoors all stages are present at once. Treat weekly and check every three to four days until two checks in a row find nothing.

Mealybugs do not go away on their own indoors. Left alone, the population grows until new shoots stay small and leaves yellow.

Not to people or pets. Mealybugs feed only on plants. They do not bite, and touching them leaves at most a greasy smear on your fingers.

For plants it depends on numbers. A few barely trouble a strong plant. A large infestation stunts new growth, yellows leaves and covers them in honeydew and sooty mold, and a heavy infestation can kill a plant. Root mealybugs weaken a plant with nothing visible on the leaves.

Whether a plant itself is a problem around pets is covered in its own care guide.

Keep every new plant apart for about 30 days and look into its leaf joints and under the pot rim when you water.

Inspect plants before you buy them, and leave behind any you could not clean.

Leave a little space between pots. Crowded plants let crawlers walk across.

Keep ants away from your plants. They protect mealybugs from their enemies.

Check prone plants (succulents, hoya, orchids) once a month, especially in winter.

When an infestation is severe, extension services advise throwing the plant away rather than treating it again and again, especially an easily replaced one or an old plant that keeps reinfesting the rest. Bag it before you carry it out.

A valuable plant is worth saving: cut out the worst parts, repot it into fresh mix in a clean pot if there are root mealybugs, and work through steps 1 to 8.

Leaves deformed or yellowed by feeding do not recover. New growth tells you the plant is through it.