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Scale Insects

Garden pest · Coccomorpha

Description​

Scale insects are small, sap-feeding insects that settle on garden and houseplants. Adults often look like bumps on leaves, twigs, or stems rather than insects. Armored scales sit beneath a separate, often hard covering; soft scales have a waxy body covering and commonly produce sticky honeydew. Females of many species remain in one place, while the young, called crawlers, move around before settling and feeding. Their colors and shapes vary widely, from flat, pale discs to rounded brown domes. Heavy infestations can weaken plants, yellow leaves, slow growth, and cause leaf drop. Honeydew from soft scales can support black sooty mold on nearby surfaces. Scale insects occur on many ornamentals, fruit trees, and indoor plants. They are often introduced on infested plants and can spread when crawlers move between plants. Damage tends to develop gradually, so an infestation may become established before it is noticed.

Symptoms​

  • Yellowing leaves
  • Sticky residue on leaves
  • Black sooty coating
  • Stunted growth
  • Leaves dropping
  • Insects visible on the plant

How to Identify​

Look closely along stems, leaf veins, and leaf undersides for clusters of small, attached bumps that do not move when disturbed. Depending on the species, they may be brown, white, gray, or waxy. Gently lift one with a fingernail: an armored scale's cover may come away separately from the insect beneath it. Soft scales may leave sticky honeydew, often accompanied by ants or black sooty mold; armored scales generally do not produce honeydew. Unlike ordinary bark markings or mineral deposits, scales can usually be lifted off, and live individuals contain soft tissue. Check nearby growth for tiny, moving crawlers.

Prevention​

Inspect new plants carefully, especially stems and leaf undersides, and keep suspect plants apart from established ones until you are confident they are clear. Check vulnerable plants regularly so small infestations are found before they spread. Avoid excessive nitrogen fertilizer, which can encourage tender growth attractive to some scales. Provide suitable light, water, and growing conditions to help plants tolerate feeding. Prune dense growth when appropriate to improve access for inspection and treatment. Preserve lady beetles, lacewings, parasitic wasps, and other natural enemies by avoiding unnecessary broad-spectrum insecticides. Ants may protect honeydew-producing scales from predators, so manage ants when they are present. Clean tools after working with infested plants and dispose of heavily infested prunings rather than leaving them nearby.

Treatment​

For a small infestation, scrape or wipe scales off by hand; prune and dispose of badly infested twigs if the plant can tolerate it. A cotton swab lightly moistened with rubbing alcohol can help remove individual scales, but test a small area first because foliage may be damaged. Encourage natural predators and control ants that defend soft scales. For larger infestations, apply horticultural oil or insecticidal soap labeled for the plant and pest, thoroughly coating infested surfaces. These products work best against the mobile crawlers; oil may also suppress some settled scales. Monitor for crawlers and repeat treatments according to the label. Avoid spraying during extreme heat or when plants are stressed, and test sensitive plants first. Dormant oil may be an option for suitable deciduous plants in the dormant season. If these measures fail, seek a locally approved scale-control product and follow its label, taking particular care to avoid harming pollinators.

Plants Affected​

Abelia, Aloe Vera, American Beech, American Elm, Arborvitae, Aucuba, Azalea, Bald Cypress, Banyan, Bay Leaf, Beech, Bird of Paradise, Bougainvillea, Boxwood, Burning Bush, Buxus, Camellia, Ceanothus, Cedar, Chaenomeles, Christmas Cactus, Cleyera, Coconut Palm, Cork Hemlock, Cork Juniper, Cork Pine, Cork Yew, Cotoneaster, Crown of Thorns, Cucumber Tree, Curry Leaf, Cypress, Daphne, Date Palm, Desert Rose, Elaeagnus, Elm, Eucalyptus, Euonymus, European Beech, Fir, Forsythia, Frangipani, Gardenia, Ginkgo, Green Ash, Hemlock, Hibiscus, Hickory, Holly, Holm Oak, Honeysuckle, Ilex, Indian Rubber Tree, Jacaranda, Jade Vine, Japanese Maple, Jasmine, Juniper, Kadupul Flower, Kaffir Lime Leaf, Kalmia, Kousa Dogwood, Laurel Oak, Ligustrum, Lilac, Live Oak, Lonicera, Magnolia, Mahogany, Mango, Maple, Middlemist Red, Mountain Laurel, Mulberry, Myrica, Myrtle, Nandina, Oleander, Orange, Orchid, Orchid Cactus, Osmanthus, Overcup Oak, Palm, Pin Oak, Pine, Pittosporum, Plumeria, Poncirus, Privet, Queen Palm, Quince, Ruscus, Sacred Fig, Sago Palm, Sarcococca, Saucer Magnolia, Silver Maple, Slippery Elm, Snowberry, Southern Magnolia, Star Magnolia, Sycamore Maple, Syringa, Tamarind, Tamarix, Taxus, Trumpet Vine, Tulip Poplar, Tulip Tree, Turmeric, Umbrella Magnolia, Viburnum, Weeping Fig, White Mulberry, Willow Oak, Windmill Palm, Winterberry, Wisteria, Xylosma, Yellow Poplar, Yew, Yucca, Zanthoxylum, Zelkova, Ziziphus

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