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Orchids

UF/IFAS lists scale, mealybugs, thrips and mites as the most common orchid pests, especially when orchids are grown as houseplants. The RHS names orchids, and Phalaenopsis in particular, among the plants glasshouse mealybugs favour. Orchids are one of the plants where mealybugs gather under the leaf sheaths, out of reach of a spray, so an inspection means looking into the sheaths and not only at the leaf surfaces.

Sticky honeydew, then black sooty mould on the leaves below, is often the first thing noticed. Springtails and soil mites in the bark or moss are mostly decomposers and need no treatment. Thrips and mites also attack orchids, but we have not yet sourced an orchid-specific profile for them.

crop context · phalaenopsis on a windowsill

The pests on orchids, and what to do

YEAR-ROUND

Longtailed mealybug

Two tail filaments longer than the body and no egg sacs. The beetle works less well on it than on citrus mealybug.

ReleaseCryptolaemus montrouzieri5 beetles per infested plant; expect to repeat
YEAR-ROUND

Brown soft scale

Flat brown bumps on stems and leaf midribs that do not move. It breeds all year, so every stage is present.

ReleaseRhyzobius lophanthae2–5 per infested plant, every 1–2 weeks
WET BARK OR MOSS

Springtails

Tiny jumping decomposers in the potting mix. Harmless; they mean the mix is staying wet.

ReleaseNothing to releaseNo treatment needed
IN THE POTTING MIX

Soil mites

Tiny mites in the bark that eat fungi and decaying matter. Not spider mites, and not a pest.

ReleaseNothing to releaseNo treatment needed

Season calendar

INDOORS · NORTHERN HEMISPHERE HOMES · QUALITATIVE
JFMAMJJASOND
Mealybugs & scale (breed all year)Jan: Pest pressure highFeb: Pest pressure highMar: Pest pressure highApr: Pest pressure highMay: Pest pressure highJun: Pest pressure highJul: Pest pressure highAug: Pest pressure highSep: Pest pressure highOct: Pest pressure highNov: Pest pressure highDec: Pest pressure high
Pests carried in on plants from outdoorsJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: QuietJul: QuietAug: QuietSep: Pest pressure highOct: Pest pressure highNov: QuietDec: Quiet
Release windowJan: QuietFeb: QuietMar: QuietApr: QuietMay: Release windowJun: Release windowJul: Release windowAug: Release windowSep: Release windowOct: QuietNov: QuietDec: Quiet

Starter program

For a few orchids on a windowsill, a cotton swab and rubbing alcohol will do more than any release. Beetles are worth buying for a larger collection in a warm room or conservatory, where a colony keeps coming back.

  1. ON BUYINGQuarantineKeep a new orchid apart from the others for six weeks. Check under the leaves and inside the leaf sheaths with a 10x lens.
  2. FIRST COLONYRubbing alcohol on a cotton swabDab each mealybug or scale. UC IPM uses 70% isopropyl or weaker, tested on a small part of the plant 1–2 days first. Repeat weekly.
  3. COLONY KEEPS RETURNINGCryptolaemus montrouzieri5 beetles per infested plant, onto a colony with egg sacs, in a room above 61 °F (16 °C).
  4. LIVE SCALE, CRAWLERSRhyzobius lophanthae2–5 per infested plant every 1–2 weeks. Rinse off the honeydew first, since sticky leaves hinder the beetle.

Setting up indoors

UF/IFAS advises starting with the least toxic treatment and working up only if it fails.

Look into the leaf sheaths

Mealybugs pack into the sheaths and leaf bases where a spray cannot reach. Part the leaves on every check.

Wash, then soap or oil

For heavier infestations UF/IFAS suggests washing the plant with water, or a horticultural oil or soap spray labelled safe for orchids. It may take more than one application.

Keep air moving and flowers dry

To cut down on disease, UF/IFAS recommends good air movement, not wetting the foliage and flowers, and clean tools when repotting or dividing.

Discard what you cannot clean

UC IPM advises discarding a plant if you cannot remove all the mealybugs, rather than treating it again and again.