Mealybugs
Pseudococcidae
White cottony sap-suckers that gather in leaf axils and along stems, mostly on houseplants and under glass. Dab colonies with a cotton swab dipped in soapy water and isolate affected plants.
How to know it
Soft gray insects 3–4 mm long, coated in white mealy wax with a fringe of short filaments, hiding in leaf axils, under leaf ribs and in the crowns of plants. Colonies look like scraps of cotton wool; root mealybugs do the same thing invisibly among the roots of a pot.
What you'll see
- White woolly patches wedged into leaf joints, growing points and the undersides of leaves.
- Honeydew, then sooty mold, on the foliage and on the shelf below.
- Yellowing, wilting and leaf drop out of all proportion to the number of insects visible.
- A pot plant that sulks without obvious cause — knock it out and look for white wax around the roots.
- Colonies concentrated where the plant is tightest: cactus areoles, orchid sheaths, succulent crowns.
Where it comes from
Females lay several hundred eggs in a waxy sac and the crawlers spread slowly across the plant, and along touching leaves onto its neighbors. Breeding is continuous in warm rooms and glasshouses, with no winter break — which is why an indoor infestation compounds quietly for months before it is noticed.
A pest of warmth and shelter: houseplants, conservatories, glasshouses and overwintered tender plants. Overfeeding and crowded staging make it worse; hard weather never comes to reset it.
Dealing with it
- Dab each colony with a cotton bud dipped in soapy water or dilute alcohol — slow, but it reaches where a spray cannot.
- Isolate the plant at once: mealybugs walk to neighbors along touching leaves.
- Wash small plants under a tepid shower and repeat weekly until nothing new appears.
- Introduce the mealybug ladybird Cryptolaemus under glass, where it is strikingly effective at room temperature.
- For root mealybugs, wash the rootball clean, repot into fresh compost, and bin the old.
Keeping it out
- Quarantine new houseplants for a month — almost every outbreak arrives on a bought plant.
- Keep plants spaced so leaves do not touch, and clean staging between seasons.
- Check leaf axils and crowns whenever you water; early colonies are trivially easy to remove.
- Avoid heavy feeding of tender plants in winter, which pushes exactly the soft growth they want.
- Sterilize pots and never reuse compost from an infested plant.
What it goes for
Houseplants above all — cacti and succulents, orchids, ficus, hoya, citrus — plus grapevines, tomatoes and anything overwintered under glass.
- Abiu
- Aeonium
- African Milk Tree
- African Violet
- Agapanthus
- Alocasia
- Amaryllis
- Anthurium
- Areca Palm
- Asparagus Fern
- Atemoya
- Bay laurel
- Blackberry Jam Fruit
- Boston Fern
- Bougainvillea
- Breadfruit
- Bromeliad
- Bulbine
- Calamondin
- Calathea
- Cherimoya
- Chinese Evergreen
- Christmas Cactus
- Clivia
and 85 more in the catalog
Trouble it brings with it
Who hunts it for you
- Green lacewingChrysoperla carnea Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing. Grow to recruit it: Cilantro,Cosmos,Dill,Sunflower,Yarrow
- HoverflySyrphidae Bee-mimicking flies whose legless larvae graze aphid colonies clean while the adults pollinate. A ribbon of shallow, nectar-rich flowers kept in bloom all season recruits wave after wave of them. Grow to recruit it: Calendula,Chamomile,Fennel,French marigold,Phacelia,Sweet alyssum
- Ladybird (lady beetle)Coccinellidae The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working. Grow to recruit it: Calendula,Cilantro,Cosmos,Dill,Fennel,Yarrow
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com