LATE FALL–WINTER
Fungus gnats
Small dark flies from the compost. The larvae live in wet compost, so they peak when plants use less water.
Crop hub · Indoors · Home garden
Houseplants
Clemson Extension names the major houseplant pests as aphids, mealybugs, spider mites, fungus gnats, scale and whiteflies, with thrips less common. The RHS finds sap feeders most often on citrus, orchids, and succulents including cacti. They are often brought into the home on a new plant, or on one that spent the summer outside.
Some things in the compost are not pests at all. Springtails and soil mites feed on fungi and decaying matter; a lot of them means the compost is staying wet. Below are the pests in the order people usually meet them, what to release where a release makes sense, and the checks that stop most problems before they start.
crop context · mixed houseplants on a windowsill
The pests you are most likely to meet
YEAR-ROUND
Mealybugs
White, waxy colonies in leaf joints and under leaves. They breed all year indoors and leave sticky honeydew.
HOT, DRY SPELLS
Two-spotted spider mite
Fine pale speckling on the upper leaf, mites beneath, and webbing once numbers are high.
YEAR-ROUND
Brown soft scale
Flat brown bumps on stems and midribs that do not move. The first sign is usually a sticky leaf or windowsill.
ON NEW PLANTS
Greenhouse whitefly
Tiny white moth-like adults lift off when the plant is touched; nymphs feed unseen under the leaves.
ON NEW GROWTH
Green peach aphid
Soft green colonies on shoot tips. Leaves yellow, curl and turn sticky.
ON FLOWERING PLANTS
Western flower thrips
Silvery, flecked leaves and white-flecked petals, common on African violet, streptocarpus and cyclamen.
WET COMPOST
Springtails
Harmless decomposers that jump when disturbed. They are a sign of overwatering, not a pest.
ReleaseNothing to releaseLet the compost dry between waterings
YEAR-ROUND
Banded palm thrips
Silvering on palms, ficus, dracaena and schefflera; dark adults with banded wings under the leaves.
Season calendar
INDOORS · NORTHERN HEMISPHERE HOMES · QUALITATIVE| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Fungus gnats | Jan: Pest pressure high | Feb: Pest pressure high | Mar: Building | Apr: Quiet | May: Quiet | Jun: Quiet | Jul: Quiet | Aug: Quiet | Sep: Building | Oct: Pest pressure high | Nov: Pest pressure high | Dec: Pest pressure high |
| Mealybugs & scale (breed all year) | Jan: Pest pressure high | Feb: Pest pressure high | Mar: Pest pressure high | Apr: Pest pressure high | May: Pest pressure high | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Pest pressure high | Dec: Pest pressure high |
| Spider mites | Jan: Building | Feb: Building | Mar: Building | Apr: Building | May: Building | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Building | Oct: Building | Nov: Building | Dec: Building |
| Pests carried in on plants from outdoors | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Quiet | Jun: Quiet | Jul: Quiet | Aug: Quiet | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Quiet | Dec: Quiet |
| Release window | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Release window | Jun: Release window | Jul: Release window | Aug: Release window | Sep: Release window | Oct: Quiet | Nov: Quiet | Dec: Quiet |
- Pest pressure high
- Building
- Release window
- Quiet
- Fungus gnats · high pressure Jan–Feb, Oct–Dec
- Mealybugs & scale (breed all year) · high pressure Jan–Dec
- Spider mites · high pressure Jun–Aug
- Pests carried in on plants from outdoors · high pressure Sep–Oct
- Release window · release May–Sep
Starter program
Most houseplant problems are solved without buying insects: quarantine, a lens, a cotton swab and a drier compost surface. Releases earn their cost in a sunroom, conservatory or plant room with a lot of plants, kept warm. The RHS warns that mealybug predators and parasitoids need warmth and, under glass, are only likely to work from May to September.
- ON BUYINGQuarantineKeep new plants, and any coming back in from summer outdoors, away from the others for six weeks and check them weekly with a 10x lens.
- FUNGUS GNATSSteinernema feltiaeOnly if drying the top 1–2 in (2.5–5 cm) of compost between waterings has not worked. 5 million nematodes treat about 25 houseplants, watered in.
- FIRST MEALYBUGSCryptolaemus montrouzieri5 beetles per infested plant, onto a colony with egg sacs, in a room above 61 °F (16 °C). Dab small colonies with rubbing alcohol instead.
- SPIDER MITE CONFIRMEDPhytoseiulus persimilis2–50 /m² per release onto the infested plants. It needs humid air to establish, so isolate the plant and mist it.
Setting up indoors
Clemson Extension's advice is that prevention is almost always easier than getting rid of an established infestation.
Quarantine every new plant for six weeks
Check the plant and its pot before buying. A plant that summered outside can bring pests in through the drainage holes, so it gets the same treatment.
Let the top 1–2 inches of compost dry
Wet compost breeds fungus gnats and springtails. Plants use less water in fall and winter, so water less often then.
Wash smooth-leaved plants every 2–3 weeks
Rinsing or wiping the leaves discourages pests, and a forceful spray of water on the leaf undersides knocks back spider mites.
Know when to throw a plant out
UC IPM and the RHS both suggest discarding a heavily infested plant rather than treating it again and again. Check that a pesticide's label allows indoor use; otherwise treat the plant outdoors and let it dry before bringing it in.