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A schefflera indoors is attacked by a very short list. Spider mites take the plant in dry, warm, still air, usually over a heated winter or a hot summer with the windows shut. Scale insects arrive on a new plant or blow in from an open window and settle along the stems and leaf stalks. Between them they cause the great majority of the leaf drop, stickiness and dull gray foliage people bring to a search engine.
Both are quiet at the start. Neither chews a hole you can see across the room. What you notice first is a change in the overall look of the plant, so the habit worth building is a monthly two-minute inspection with the leaves turned over rather than waiting for damage.
| What you see | Most likely cause | Where to look to confirm |
|---|---|---|
| Fine pale speckling over the leaf, color washing out | Spider mites | Leaf undersides, along the midrib |
| Sticky shine on leaves and the floor below | Scale, or aphids on new growth | Leaf stalks and the underside of the midrib |
| Black sooty film on the upper leaf surfaces | Sooty mold growing on pest honeydew | Find the pest above the affected leaves |
| Fine webbing in the leaf joints | Spider mites, already advanced | The growing tips and the leaf junctions |
| Small brown limpet-like bumps that do not rub off | Scale insects | Stems, leaf stalks, the underside of the midrib |
| White fluff in the crotches of the stems | Mealybugs | Where a leaf stalk meets the stem |
Turn a leaf over and look at it against the light. Spider mite speckling is visible from above as a washed-out cast long before you can see the mites themselves.
Spider mites: dry air and still air
Spider mites breed fastest in warm, dry, still conditions, which describes a room with the heating on all winter almost exactly. From a handful of mites to a plant covered in webbing takes about three to four weeks at 77F (25C), so the difference between catching them early and catching them late is only a couple of inspections.
They feed by puncturing cells on the leaf underside, so the damage reads as thousands of tiny pale dots rather than as holes. Once whole leaves have gone pale and papery those leaves will not recover; the aim of treatment is to protect the leaves that are still green.
- Wash the undersides first Take the plant to a shower or use a spray bottle and blast the leaf undersides with plain water, working from the bottom of the plant upward. This alone removes most of a light infestation and it costs you nothing. Repeat every three or four days for two weeks.
- Wipe the leaves individually On a plant small enough to handle, support each leaflet with one hand and wipe both surfaces with a damp cloth. Rinse the cloth often. It is slow, but on a badly hit plant it removes eggs that a spray misses.
- Treat with a horticultural soap or oil Spray to run-off, covering the undersides properly, and repeat at five to seven day intervals for at least three applications. One application never works: it kills the mobile mites and leaves the eggs, which hatch within a week.
- Raise the humidity around the plant Group plants together, stand the pot on a tray of damp gravel with the pot base clear of the water, and mist the undersides. Mites struggle in humid air, so this changes the conditions rather than just killing what is there.
- Quarantine while you treat Move the plant away from other houseplants until you have gone a fortnight with no new speckling. Mites walk and drift between touching plants easily.
Do not spray oil on a plant standing in strong direct sun or on a plant that is bone dry at the roots. Water it the day before and treat it out of the sun, or you will scorch the leaves with the treatment.
Scale: the stickiness comes first
Scale insects sit still under a hard or waxy shell and suck sap. The shell is what makes them hard to kill with a contact spray, and it is also why people mistake them for a natural bump on the stem. On a schefflera they concentrate on the leaf stalks, the underside of the midrib and the woody main stems.
The tell is stickiness. Scale excretes honeydew, which lands on the leaves below and on the floor, table or windowsill under the plant. If your plant has become sticky, you have scale or aphids somewhere above the sticky surface, and the pest is always upward of the mess.
Sooty mold is the black film that then grows on the honeydew. It is not attacking the plant, it is living on the sugar, but it blocks light and holds the leaf in permanent shade. Killing the pest stops new mold; the existing black film has to be wiped off by hand.
- Scrape the adults off Rub each scale off with a thumbnail, an old toothbrush or a cotton bud dipped in surgical spirit. On a schefflera with a countable number of stems this is realistic and it is the single most effective thing you can do.
- Go over every leaf stalk Work through the plant stem by stem rather than sweeping over it. Scale hides in the joint where the leaflets radiate from the top of the stalk, and a plant declared clean usually still has some there.
- Follow with a horticultural oil An oil spray smothers the crawler stage, which has no shell yet. Spray thoroughly, including stems, and repeat twice at ten day intervals to catch successive hatches.
- Wipe off the sooty mold Once the pest is gone, wash the black film off with a damp cloth and a drop of mild soap, supporting each leaf. Leaves left black stay black, and they contribute almost nothing to the plant.
- Cut out a stem that is encrusted If one branch is solid with scale and defoliated, cut it out and bin it rather than trying to save it. Removing the reservoir is faster than treating it.
Leaf drop that is not a pest
A schefflera drops leaves readily, and half the time it is not an insect at all. Before you spend a month spraying, check the leaf undersides once carefully. If they are clean, the cause is on this list instead.
| Trigger | How it looks | What to do |
|---|---|---|
| A sudden move to a darker spot | Lower and inner leaves yellow and drop over two or three weeks | It is adjusting. Hold the position and stretch the watering |
| Cold draft from a door or window | Green leaves drop with no yellowing, on the draft side | Move it out of the airflow |
| Compost kept permanently wet | Yellowing from the bottom, soft base, sour smell | Let it dry hard, then check the roots |
| Bone dry at the roots | Leaflets fold down, then drop in a rush | Water thoroughly and repeat within a few days |
| Hot dry air from a heater | Brown crisp tips, then whole leaves | Move it away from the vent and raise humidity |
| Repotted into a much bigger pot | Slow decline, no new growth, wet compost | Pot back down a size into fresh mix |
Losing one or two of the oldest, lowest leaves over a season is normal turnover on a schefflera, not a problem. A run of leaves going in a fortnight is.
The monthly check, and what to write down
Everything above gets easier if you catch it early, and the only way to catch it early is a routine look. Once a month, turn over three or four leaves from different heights, run a finger along two leaf stalks, and touch the surface under the plant to see whether it is sticky. That is the whole inspection.
Keep a short record as you go: the date you first saw speckling or stickiness, which pest it turned out to be, which stems it started on, what you sprayed and on which dates, and the date you last saw a live one. Two things come out of that record. First, you find that your infestations start at the same time of year, usually a few weeks after the heating goes on or the windows close for summer, and you can start misting and inspecting before it happens instead of after. Second, you can tell whether a treatment actually worked or whether you simply stopped looking.
Note the position of the plant too. Mites reliably hit the plant nearest the radiator and leave the one by the cool window alone, and that pattern is only visible once you have written it down twice.
Knowing when to give up on a plant
There is a point at which treating costs more than starting again. A schefflera that has lost most of its leaves to mites, has webbing through every joint and is standing next to your other houseplants is a source of reinfestation, not a plant in recovery.
The decision is easier if you take cuttings first. Cut two or three clean, unaffected growing tips, wash them thoroughly, root them separately, and then dispose of the parent. You keep the plant and lose the pest, which is a better outcome than six months of spraying.
Bin infested material rather than composting it, and wash the empty pot and the saucer with hot soapy water before you reuse them. Scale crawlers survive on a dry pot rim for weeks.