Scale insects are easy to miss because they do not look like insects. Most of their lives they sit still under a waxy or hard cover, lined up along stems and leaf veins like part of the plant. Sticky leaves are often the first clue.

This page covers identification, soft versus armored scale, the life cycle, damage and control from least toxic up. For a side-by-side view of all the common pests, see our houseplant pest overview.

How to identify scale

UC IPM describes scales on houseplants as small, brown or greyish, mostly stationary insects with a waxy, shell-like body or a hard protective cover. Adults have no obvious head or legs. Iowa State says they often line up along stems and leaf veins, typically on the underside.

Sizes vary by species. Clemson gives 1.5–13 mm (1/16–1/2 in) across. Maryland says the two most common indoor species reach up to 4.75 mm (3/16 in).

The young are different. UC IPM says crawlers are tiny, usually yellow to orange, and have legs. They walk to a feeding spot and settle within a day or two.

Soft scale vs armored scale

The two groups need different treatment, so it is worth telling them apart.

Soft scaleArmored scale
ShapeRounded, convex (domed); up to 6 mm (1/4 in) (UC IPM)Flat, platelike; under 3 mm (1/8 in) (UC IPM)
Lift testCovering is the body; it lifts off whole (UC IPM, Clemson)Cover lifts off and the insect stays on the plant (UC IPM, Clemson)
HoneydewYes, often lotsNone
IndoorsMost common on houseplants (UC IPM, Colorado State)Much less common (Colorado State)
Systemic imidaclopridControls most soft scales (UC IPM)Does not control most armored scales (UC IPM)

Common indoor species

Maryland Extension describes the two you are most likely to meet:

  • Brown soft scale (Coccus hesperidum). Oval covers, light tan, yellow-green or yellow-brown with darker mottling. Crawlers are yellow. Found along veins, on leaf undersides and petioles, and hidden under leaf sheaths.
  • Fern scale (Pinnaspis aspidistrae), an armored scale. Flat, pear- or oyster-shell-shaped brown female covers. Males are white, elongated and ridged. As numbers grow, Maryland says the males create white flecking or a snowy coating on the leaves.

Colorado State adds hemispherical scale (Saissetia coffeae) as another soft scale on houseplants.

Look-alikes

  • Fern spore clusters. UC IPM warns scale on fern fronds can be mistaken for spores. Look for honeydew, sooty mould, white male covers or yellow spotting, which spores do not cause (Maryland).
  • Mealybugs. White and waxy, but they walk slowly. See our pothos mealybug guide.
  • Whitefly nymphs. UC IPM lists them as scale look-alikes. Adult whiteflies fly up nearby. See our hoya whitefly guide.

Life cycle

UC IPM says scales hatch from eggs, usually hidden under the female’s body, and develop through two nymph stages before adulthood. Crawlers settle and then stay put. Colorado State says brown soft scale eggs hatch under the mother over several weeks, and the scales grow for two to four months, rarely moving in later stages.

Maryland gives about 60 days per generation for brown soft scale, with three to seven overlapping generations a year indoors. Fern scale takes about 95 days, with at least two generations a year. The RHS says indoor scales breed all year round.

This matters for treatment. Colorado State says crawlers are the vulnerable stage, and treatment has to keep covering the plant through a whole generation of two to four months.

Which houseplants get scale

Maryland lists a long host range for brown soft scale, including orchids, bromeliads, hoya, hibiscus, ferns, palms, dieffenbachia, pothos, peace lily, anthurium, monstera, philodendron, ficus, peperomia, schefflera, croton, aloe, dracaena, citrus, rosemary and coffee.

For fern scale, Maryland lists ferns, palms, air plants, alocasia, cast-iron plant, asparagus fern, ficus, fittonia, croton, snake plant and dracaena. Colorado State says soft scale problems are most frequent on ficus, citrus, ferns and ivies.

Plant-specific guides: pothos scale, schefflera pests, croton pests and sticky honeydew on indoor citrus.

Damage signs

  • Honeydew. Maryland says sticky honeydew on leaves or on surfaces under the plant is the main sign of soft scale. It can stop new leaves unfurling properly.
  • Sooty mould. Black film growing on the honeydew (UC IPM).
  • Yellowing and leaf drop. Maryland lists yellowing, early leaf shed and stunting.
  • Yellow spotting. Moderate fern scale infestations cause yellow spots (Maryland). Colorado State says many armored scales cause spotting around the feeding site.
  • Dieback. Heavy, prolonged infestations of either group can cause dieback (Colorado State, Maryland).
  • Ants visiting the plant, drawn by honeydew (Maryland).

Control, least toxic first

1. Isolate the plant

Maryland says to quarantine plants with scale. Keep it apart until new growth stays clean.

2. Scrape them off

Maryland says scales should flake off with pressure from a fingernail, toothpick, cotton swab or soft toothbrush. Colorado State notes that even a minor disturbance can break a settled scale’s mouthparts so it starves. Removing them also makes it easier to see whether numbers rebound.

UC IPM suggests pruning out heavily infested parts and washing crawlers off with water.

3. Alcohol on a swab

Iowa State suggests spot-treating a few scales with a cotton swab dipped in rubbing alcohol. Colorado State says alcohol and soap give some control, mainly on crawlers and very young scales. Test on a small area first, because alcohol can burn leaves.

4. Horticultural oil or insecticidal soap

Colorado State calls spray oils the most effective treatment for scales, and the most effective for armored scale. UC IPM says oil and soap work best on small immature nymphs. Clemson says adults are protected by their covering, while crawlers are susceptible.

  • Repeat. Maryland says multiple treatments are usually needed. Iowa State suggests weekly applications for four to six weeks, because nymphs hatch on a rolling basis.
  • Check the label for your plant. Maryland says ferns are sensitive to many ingredients but tolerate horticultural oil if kept shaded while the spray dries.
  • Do not spray in heat. UC IPM’s scale note says not to apply oil above 32 °C (90 °F).

See our neem oil guide and neem oil vs insecticidal soap comparison.

5. Systemic insecticides: soft scale only

UC IPM’s houseplant note says a soil-applied systemic, as a drench or granules, is effective against some soft scales. Maryland lists a systemic product labeled for indoor plants, typically imidacloprid, as effective on brown soft scale only. Colorado State says imidacloprid should work on most soft scale infestations.

It is not a fix for armored scale. Colorado State says systemics give poor control of armored scales and may increase spider mites. Maryland says systemic products are not labeled for edible indoor plants such as citrus fruit and herbs.

When to discard the plant

Maryland says heavily infested plants are best discarded. Iowa State says destroying a heavily infested plant before scale spreads is often better. The RHS suggests replacing plants heavily affected by scale.

Prevention and quarantine

  • Inspect new plants thoroughly. Maryland says both common indoor species occur worldwide and can arrive on any plant shipment.
  • Quarantine new arrivals. Colorado State suggests at least three weeks; Clemson suggests six weeks with weekly checks.
  • Check hidden spots. UC IPM says look behind leaf bases, inside leaflet folds and in flower clusters.
  • Judge success by new growth. The RHS says dead scales stay attached; clean new growth shows treatment worked.

References