close up of brown scale on an indoor plant leaf

Close up of the adults and nymphs of brown scale
Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Updated: March 13, 2023

Key points

  • Learn more about scale insect groups, biology, and management on Introduction to Scale Insects.
  • Inspect ailing plants and learn how to find scale insects using the information on Monitoring for Scale Insects.
  • Few scale species occur on indoor plants, though they may not be noticed unless plants show signs of damage. The main sign of soft scale infestation is honeydew on foliage or on surfaces under the plant.
  • Symptoms of plant damage include leaf yellowing and premature leaf shed, stunting of growth, and potentially dieback.
  • Treatment options are limited, and pesticides need to be labeled for use indoors unless treatments are applied while plants are summering outside. Quarantine plants with scale; heavily infested plants are best discarded.
drop of sticky honeydew on the leaf of an indoor citrus plant
A drop of sticky honeydew on the leaf of an indoor citrus
Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Common indoor plant scale species

Brown soft scale (Coccus hesperidum) 

This soft scale occurs worldwide, so could be present on plant shipments from any location. Inspect new houseplants thoroughly.

scale on Meyer lemon leaf
Brown scale clustered along the vein of a Meyer lemon leaf

Appearance

  • Mature female covers are oval, light tan, yellow-green, or yellow-brown with darker mottling (sometimes entirely dark brown), and up to 3/16” (4.75mm) in length.
  • Crawlers are yellow.

Common host plants

An enormous array of plants are used by this species – 400 genera in 133 families. Below are those popularly grown as year-round houseplants or as potted tropicals sheltered indoors for the winter. This scale can also infest several species of hardy outdoor garden plants.

  • Flowering houseplants; including orchids, bromeliads, wax flower (Hoya carnosa), Oleander (Nerium oleander), cyclamen (Cyclamen), Chinese hibiscus (Hibiscus rosa-sinensis), clivia (Clivia), amaryllis (Hippeastrum),  jasmine (Jasminum), gardenia (Gardenia), bird-of-paradise (Strelitzia reginae), and calla lily (Zantedeschia)

  • Foliage houseplants; including ferns, palms, banana (Musa), dumb cane (Dieffenbachia), pothos (Epipremnum), peace lily (Spathiphyllum), other aroids (Anthurium, Monstera, Philodendron, Syngonium), fig/Ficus (Ficus), peperomia (Peperomia), begonia (Begonia), strawberry begonia (Saxifraga stolonifera), Schefflera (Schefflera), ivy (Hedera), croton (Codiaeum variegatum), aloe (Aloe), haworthia (Haworthia), agave (Agave), corn plant (Dracaena), and ti plant (Cordyline fruticosa)

  • Edible tropicals;  including citrus (Citrus), rosemary (Rosmarinus officinalis), pomegranate (Punica), olive (Olea), coffee (Coffea arabica), and bay laurel (Laurus nobilis)

Where to look

  • On foliage, particularly along leaf veins, on the leaf underside, or on leaf petioles. May also occur on young stems/branches.
  • Hidden underneath leaf sheaths (such as on orchids) or in crevices between emerging leaves.

Plant damage

  • Moderate to heavy infestations will produce large quantities of honeydew, which when plants are outdoors for the summer can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold. When plants are indoors, honeydew may attract ants.
  • Honeydew’s stickiness may interfere with leaf unfurling/expansion and cause leaf deformity or tearing on delicate new growth.
  • Heavy or prolonged infestations can cause wilting and premature leaf shedding, reduced plant vigor, and potentially dieback.

Life cycle

  • One generation takes about 60 days to complete depending on ambient temperature.
  • On indoor plants, multiple overlapping generations can occur year-round. Between three and seven generations per year is typical.

Fern scale (Pinnaspis aspidistrae)

This armored scale occurs worldwide, so could be present on plant shipments from any location. Inspect new houseplants thoroughly.

The white male covers over brown female cover of fern scale.
Fern scale - White male covers and brown female covers.
Photo: J.A. Davidson, Univ. Md, College Pk, Bugwood.org

Appearance

  • Mature female covers are pear- or oyster shell-shaped, flat, light to dark brown, and up to 3/16” (4.75mm) in length.
  • Male covers are elongate, white with prominent ridges, and smaller.
  • Crawlers are yellow with red eyes.

Common host plants

A wide array of plants are used by this species – 139 genera in 71 families. Below are those popularly grown as year-round houseplants or as potted tropicals sheltered indoors for the winter. This scale can also infest multiple species of hardy outdoor garden plants, including liriope (Liriope).

  • Flowering houseplants; including orchids, African violet (Saintpaulia), Chinese hibiscus (Hibiscus rosa-sinensis), amaryllis (Hippeastrum), and bird -of- paradise (Strelitzia)
  • Foliage houseplants; including ferns, palms, air plant (Tillandsia), banana (Musa), aroids (Alocasia, Anthurium, Monstera, Philodendron, Rhaphidophora), cast-iron plant (Aspidistra), asparagus fern (Asparagus), fig/Ficus (Ficus), nerve plant (Fittonia), croton (Codiaeum), agave (Agave), snake plant (Sansevieria/Dracaena), corn plant (Dracaena), and ti plant (Cordyline fruticosa)
  • Edible tropicals; including Citrus (Citrus) and Olive (Olea)

Where to look

  • On foliage; rarely on branches or fruit
  • Sheltered underneath leaf sheaths (such as on orchids or palms) or in crevices between emerging leaves (such as in the crown of liriope).
  • Numerous males, produced in increasing proportions as the population increases, will create a prominent white flecking or snowy flocking on plant surfaces.

Plant damage

  • Ferns sometimes tolerate high populations with few symptoms.
  • Moderate infestations cause yellow spotting on foliage and potentially premature leaf shed.
  • Heavy or prolonged infestations can cause loss of vigor and deformed growth, followed potentially by plant death.

Life cycle

  • One generation takes about 95 days to complete depending on ambient temperature.
  • On indoor plants, reproduction and development occur year-round. At least two generations per year are typical.

Monitoring and Treatment

If plants are summered outdoors, beneficial parasitoids may suppress populations on brown soft scale. Look for holes in scale covers for evidence of their presence. Parasitized scale may be a different color (often black) than a healthy scale of the same age. Avoid treating parasitized scale with pesticides.

  • Physically remove scale: they should easily flake off with pressure from a fingernail, toothpick, cotton swab, or soft-bristled toothbrush. This not only immediately reduces the population but also allows you to more effectively monitor any population rebounding after treatment.
  • Insecticide options are horticultural oil, insecticidal soap, or a systemic product (effective on soft brown scale only) labeled for use on indoor plants (typically imidacloprid-based). Multiple insecticide treatments are usually necessary, monitor the plant after treatment.
  • Read the product label for precautions – not all houseplants are tolerant of every pesticide. Ferns are sensitive to many ingredients, though horticultural oil can be tolerated if plants are kept shaded while the spray dries. Systemic products are not labeled for use on edible indoor plants (fruits, herbs).

Adapted in part from data on ScaleNet and information collected by UMD Professor Emeritus entomologist Dr. John Davidson.

Compiled by Miri Talabac, Horticulturalist & Coordinator, HGIC. 2022

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