Why Plants Die
Theme
Theme

Mealybugs: white, waxy clusters in the joints of houseplants

Check your plant with the questions

Tufts of white cotton tucked where a leaf meets its stem are usually the first thing people notice. Underneath that wax sit soft, slow insects drinking sap. Mealybugs rank among the commonest pests of indoor plants for a plain reason: a heated room lets them breed all year, and the parasites and predators that hold them down outdoors are absent. A light infestation found early can be cleared by hand. A heavy one spread through a large plant is often not worth the fight.

Recognizing them

What you see first is wax rather than insect: fluffy white patches in leaf axils, leaf sheaths, the crown, between twining stems and in the folds of new leaves. Some of that fluff is egg sacs; tease one open and the eggs inside are orange-pink. The insects themselves are oval, soft and visibly segmented, dusted in white powder, often with a pinkish body showing through. Waxy threads fringe their edges. Adult females are small, around a sixteenth of an inch in one extension description and up to about a sixth in the RHS account. They can walk, though slowly and not far. Check the undersides of leaves, stems close to the potting mix and the pot's outer wall as well.

Two species turn up most often indoors. The citrus mealybug has short wax filaments of even length all around and sometimes a darker stripe along its back. The longtailed mealybug trails two threads longer than its own body, and it bears live young instead of laying eggs in cotton.

Newly hatched young, called crawlers, are yellow, orange or pink, bare of wax and quite mobile; once they settle to feed they begin coating themselves.

Look-alikes

  • Cottony cushion scale and soft scales. These are close relatives that also leave honeydew. Most mealybugs keep working legs and can shift position, whereas scales sit under a cover. See scale.
  • Woolly aphids and whiteflies. Both make wax and honeydew of their own, so scrape back the fluff and look at the insect under it before deciding.
  • Mealybug destroyer larvae. The young of this predatory lady beetle wear a white waxy coat and look like oversized mealybugs. If these beetles were released nearby, the unusually big "mealybugs" in a colony may be working for you.
  • Root mealybugs, a separate group living in the potting mix on the roots. They lack the wax fringe and usually stay hidden until the plant is unpotted.

What they do to a plant

Each insect draws sap from the phloem, and a crowd of them drains the plant's vigor. Dense colonies slow growth, yellow the foliage and make leaves drop; in bad cases shoots die back or the plant dies. The citrus mealybug also injects a toxin as it feeds, which can leave growth misshapen. Sugar the insects cannot use comes out as honeydew, making foliage and stems sticky; black sooty mold then grows on it, and ants may arrive to harvest it. A healthy plant copes with a handful, but numbers climb fast when nobody looks.

How they get in

Usually on another plant. Adult females cannot fly and crawl only short distances, so a colony seldom arrives on its own; it comes with a new purchase, a cutting, a reused pot, or a stake or tool that touched an infested plant. From there they walk across wherever leaves overlap. Indoors they breed through the year, more slowly in winter, and in midsummer the young can mature in about a month. Heavy nitrogen fertilizer makes matters worse, because it forces soft new shoots, and those are what egg-laying females seek out.

What to try first

  1. Move the plant away from the rest. Separating it limits the spread while you work.
  2. Take off what you can reach. Pick off colonies, or prune out shoots where they are packed in. Bag the trimmings at once: cut pieces keep mealybugs alive until they dry out. Look over the pot, saucer and any stakes too, and discard items carrying egg sacs.
  3. Dab the rest with rubbing alcohol. A cotton swab dipped in isopropyl alcohol thinned with water kills or lifts off each insect it touches. Test it on one leaf a day or two ahead, because some plants scorch, and keep it on the insects rather than the foliage.
  4. Rinse sturdy plants. A firm stream of lukewarm water dislodges many exposed mealybugs. Repeat every few days; one wash leaves survivors.
  5. Use soap or oil against the young. Insecticidal soap, horticultural oil and neem oil act mainly on crawlers and young nymphs that carry little wax, and only where the spray lands. Soak the leaf joints and sheaths, test a small patch first, and expect several rounds.
  6. Keep systemic products for later. Spikes or granules containing imidacloprid can cut crawler numbers on houseplants, but UC IPM finds them less dependable on mealybugs than on most other sap-sucking insects and advises against them on flowering plants, to spare pollinators and natural enemies.
  7. Know when to stop. Where a plant is infested throughout, both UC IPM and the RHS suggest that discarding it can be less work than treating it again and again.

The mealybug destroyer and several parasitic wasps are sold for release in greenhouses. They need warmth, and the beetle needs plenty of egg sacs before it will breed, so they suit a greenhouse with a heavy outbreak better than a single pot on a windowsill.

Signs of progress

Mealybugs hit with alcohol go light brown, which shows which ones you reached. Parasitized ones turn darker and may carry a tiny exit hole. Look the plant over each time you water, paying attention to leaf joints and new growth: fresh white fluff means eggs have hatched. No treatment reaches every insect, so a second or third round is normal rather than a failure. Because young can mature within about a month in summer, keep checking for several weeks after you last saw a live one, and check any plant whose leaves touched it.

Plants whose sources name mealybugs

On this site, 193 plants list mealybugs as a pest in the NC State Extension or RHS page they draw on. The list here is generated from that data, not written by hand. Among houseplants, UC IPM singles out cacti, jade, hoya, orchids, palms, ficus, dracaena, schefflera and poinsettia as frequent hosts.

A plant that is declining with no wax anywhere above the pot may have root mealybugs instead. Sticky leaves with shell-like bumps rather than cotton point to scale. For anything else, run the diagnosis.

Answer a few questions about your plant

Sources

This page is written for this site from the sources above; it quotes none of them. It has not seen your plant.