Scale Insects: Armored vs Soft Scale and When to Treat
Scale insects are tiny sap-sucking insects that settle on stems, bark and leaves and hide under a waxy cover, so they look like bumps rather than bugs. The two common kinds behave differently: armored scales have a cover that lifts off the insect and make no honeydew, while soft scales are part of their own cover and drip sticky honeydew that grows black sooty mould. Treat the mobile crawler stage, usually with horticultural oil or insecticidal soap, because settled adults are protected.
Most failed scale treatments fail for one of two reasons: the spray went on when only protected adults were present, or the product was wrong for the type of scale. Both are avoidable once you know which family you have and when its crawlers move.
What is a scale insect?
Scale insects belong to the superfamily Coccoidea, about 8,000 described species according to University of Wisconsin Extension, and are close relatives of aphids and whiteflies. Adult females are wingless and usually show no obvious head, legs or antennae; UC IPM describes them as circular, elongate or oval discolorations or bumps on bark, leaves or fruit, with covers from 1/25 to 1/4 inch long (about 1 to 6 mm). Adult males are rarely seen: tiny, gnat-like and unable to feed.
The only stage that walks is the crawler, the first nymph stage, usually yellow to orange. UC IPM says crawlers settle and begin feeding within a day or two of emerging; in most species they then lose their legs and never move again.
Armored vs soft scale: the test that decides everything
| Armored scale (Diaspididae) | Soft scale (Coccidae) | |
|---|---|---|
| Size | Usually 1/16 to 1/8 in (1.6 to 3.2 mm) | Usually 1/8 to 1/4 in (3.2 to 6.4 mm), a few to 1/2 in |
| Shape | Flat, platelike, often with a raised “nipple” and rings | Rounded, convex, like a tiny tortoise shell |
| Flip the cover | Cover lifts off; the soft yellow or orange body stays on the plant | Cover and insect come off together; the cover is the body wall |
| Honeydew and sooty mould | None | Yes, often heavy, and ants tend it |
| What it feeds on | Contents of individual plant cells | Phloem sap |
| Generations a year | Usually several | Usually one |
| Imidacloprid | Does not control most species | Controls most species |
| Common examples | Euonymus, oystershell, San Jose, pine needle scale | Brown soft, lecanium, magnolia, Fletcher, cottony maple scale |
Compiled by The Pest Control Brief from UC IPM Pest Notes: Scales (Publication 7408), University of Wisconsin Extension and University of Maryland Extension.
To run the test, slide a fingernail or knife tip under one bump. If a cover comes away and leaves a soft body behind, it is armored. If the whole thing lifts as one piece, it is soft. Sticky leaves, a sticky floor under a houseplant, black mould or a stream of ants up the trunk all point to a soft scale or another honeydew producer. White bumps are usually cottony egg sacs, pine needle scale, the small white males of euonymus scale, crape myrtle bark scale sacs or mealybugs.
What do scale insects look like on common plants?
| Scale | Type | Main hosts | What you see | Crawlers (NJ calendar) |
|---|---|---|---|---|
| Euonymus scale | Armored | Euonymus (especially E. japonicus), bittersweet, pachysandra | Grey to brown females; masses of small white males under leaves | June, again July |
| Oystershell scale | Armored | Ash, dogwood, lilac, maple, willow | Grey to brown, shaped like a tiny oyster shell | Late May |
| San Jose scale | Armored | Fruit and nut trees, many shrubs | Round, grey, with a raised black centre spot | June, mid-July, September |
| Pine needle scale | Armored | Pines and other conifers | White, 1/8 inch, oyster-shaped, on needles | Mid-May, July |
| Magnolia scale | Soft, native | Magnolias only | About 12 mm, pinkish-orange to brown with white wax, on twigs | Late August to September (Penn State) |
| Cottony maple scale | Soft | Maples and other shade trees | White cottony egg sacs in early summer, like strung popcorn | Mid-June |
| Brown soft scale | Soft | Houseplants: gardenia, fern, camellia, fig | Flat, oval, mottled brown, up to 1/8 inch | Year round indoors |
| Crape myrtle bark scale | Felt scale (Eriococcidae) | Crape myrtle | White felty sacs on bark that bleed pink when crushed | Mid-April to May, again late summer (Clemson) |
Compiled by The Pest Control Brief from University of Wisconsin Extension, UC IPM, Penn State Extension, Clemson HGIC and the New Jersey Department of Agriculture HPRC Vol. III scale table.
Are scale insects harmful to plants?
Sometimes. UC IPM is clear that plants are not harmed by a few scales and that even high populations of certain species apparently do no damage, while others kill their host. Heavy infestations cause yellowing, early leaf drop, twig dieback and a scorched look where dead leaves stay on killed branches. Armored scales tend to hurt the host more than soft scales, Wisconsin notes, because toxins injected while feeding kill cells around the feeding site.
Soft scales do a second kind of harm. Their honeydew coats leaves, cars and patios, and sooty mould on top shades the leaf. The mould does not infect the plant, University of Maryland Extension says, but it can take a while to weather away after the scales are gone. Ants that farm the honeydew also protect the scales from their predators, which is why controlling ants is part of controlling scale.
Where do scale insects come from?
Usually from another plant. UC IPM says crawlers walk over plants, blow on the wind, or are carried by people and birds. Nursery stock moves them furthest: Penn State notes that crape myrtle bark scale infestations are scattered across the Southeast rather than spreading as a front, which suggests it travels mainly on infested nursery plants. Indoors, Missouri Botanical Garden advises isolating new houseplants for two to three weeks and checking plants that summered outdoors before they come back in.
Crape myrtle bark scale
This Asian felt scale was first found in Richardson, Texas, in 2004. UF/IFAS listed 12 states as of spring 2018: Alabama, Arkansas, Georgia, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, Tennessee, Texas, Virginia and Washington. Clemson confirmed South Carolina in 2019, and Penn State’s 2025 map, drawn from EDDMapS, shows 14 states and Washington, D.C., plus specimens in Pennsylvania. Counts differ between sources, so check EDDMapS or your state extension service for the current picture. Females are up to 2 mm long and lay 100 to 300 pink eggs in white felty sacs; in the South there are two to four overlapping generations a year. It rarely kills the tree but cuts flowering and blackens trunks with sooty mould.
Our iNaturalist analysis has only about 400 US research-grade records of crape myrtle bark scale, too few to map by state reliably, but the timing is clear: records peak in September and October, after the late-summer crawler peak that Clemson describes.
When to treat scale: follow the crawlers
Every extension source makes the same point: settled adults are protected by wax, so contact sprays work on crawlers. University of Maryland Extension calls the crawler the stage most vulnerable to insecticides. Timing differs widely between species, which is why identification matters. New Jersey’s nursery inspectors time crawlers by growing degree days, the heat accumulated above 50°F since spring.
Monitor with double-sided tape
UC IPM’s method is simple and cheap:
- In spring, before crawlers appear, wrap transparent double-sided sticky tape tightly around several infested twigs, folding over the loose end.
- Replace the tape weekly and keep the old strips between white paper and clear plastic, labelled by date.
- Crawlers show as yellow or orange specks; use a hand lens to tell them from pollen and dust.
- Spray after crawler numbers on the tape have peaked and definitely begun to decline, which is soon after most have settled.
Is the scale already dead?
Dead scales do not fall off, so a branch can look infested for months after a treatment worked. Wisconsin’s test: crush one. Dry means dead; juicy, or a streak on paper, means alive. Clemson uses the same test on crape myrtle bark scale, which bleeds reddish fluid only while alive. UC IPM adds that a round exit hole in a cover means a parasitic wasp has already killed it, and if most scales are dead or parasitised, it advises delaying any spray.
How to get rid of scale insects
| Option | Armored scale | Soft scale | Notes from extension sources |
|---|---|---|---|
| Dormant oil (winter, on bare deciduous plants) | Good on overwintering stages | Good | Not for oystershell or olive scale, whose susceptible stages are absent in winter |
| Horticultural oil in the growing season | Good on crawlers; needs thorough coverage | Good on crawlers | Not below 32°F, above 90°F, above 90 per cent humidity or with rain due in 24 hours |
| Insecticidal soap | Crawlers only | Crawlers and young nymphs | No residual action; Wisconsin advises at least three treatments six to seven days apart |
| Imidacloprid (soil-applied systemic) | Does not control most armored scales | Controls most soft scales | May cause outbreaks of cottony cushion scale; some systemics trigger spider mite outbreaks |
| Dinotefuran (systemic) | Controls most types | Controls most types | Penn State names it the most effective drench for crape myrtle bark scale |
| Broad-spectrum sprays (carbaryl, malathion, pyrethroids) | Avoid | Avoid | UC IPM: highly toxic to natural enemies and can trigger mite outbreaks |
| Scrubbing, pruning, replacing the plant | Yes | Yes | UC IPM: prune heavily infested twigs on small plants; Maryland: replace small plants that are heavily infested |
Compiled by The Pest Control Brief from UC IPM Pest Notes: Scales, University of Wisconsin Extension, Penn State Extension and University of Maryland Extension. Follow the product label for every use.
Why systemics work poorly on armored scale
The feeding table explains it. University of Maryland Extension says soft scales feed on phloem sap, the plant’s sugar stream, while armored scales feed on the contents of individual plant cells. A systemic carried in sap reaches a soft scale reliably and an armored scale much less so, which fits UC IPM’s finding that imidacloprid controls most soft scales but not most armored scales. Wisconsin adds that soil systemics on large woody plants can give poor control because the product moves unevenly. Systemics can also reach flowers, so UC IPM advises waiting until plants and nearby plants have finished flowering; our guide to pollinator protection rules covers the label side.
Natural enemies and ants
Many scales are held in check by tiny parasitic wasps and lady beetles, including the twicestabbed lady beetle, which UC IPM says can be easily overlooked. Broad-spectrum sprays and dust disrupt them, and ants defend scales from them. UC IPM recommends a 2 to 6 inch sticky band on a wrapped trunk, pruning branches that bridge to buildings, and enclosed ant baits. It may take several months, or until the next season, before conserved natural enemies bring numbers down.
For the wider principle of why a garden spray can make pests worse, see our explainer on why a pest control company will not spray your vegetables. Scale is rarely a call for a structural pest control company; a certified arborist or plant health care service is the usual professional for large trees.
Scale on houseplants
Indoors, soft scales are the main problem, and Wisconsin names brown soft scale and hemispherical scale among the commonest on houseplants. For light infestations, Wisconsin suggests a soft toothbrush or cotton swab dipped in soapy water or 70 per cent isopropyl alcohol, repeated weekly, probably several times. Missouri Botanical Garden adds highly refined horticultural oil, which can kill both adults and crawlers. A badly infested plant is often better discarded. Our houseplant pests guide covers mealybugs, spider mites and fungus gnats alongside scale, and our review of neem oil trials explains what neem does and does not do.
Are scale insects mealybugs?
Mealybugs are scale insects in the broad sense. UC IPM places mealybugs in the family Pseudococcidae within the superfamily Coccoidea, which also includes armored and soft scales, and describes them as soft, oval, wax-covered insects closely related to soft scales but without the scale covers. Like soft scales, they produce honeydew.
Do scale insects live in the soil?
A few do. Ground pearls (Margarodes) are scale insects that live on grass roots in the Southeast and Southwest. NC State Extension describes the nymphs as hard, yellowish-purple pearls up to 1/16 inch across that suck root juices, causing dead patches in centipede, St. Augustine, zoysia and Bermuda grass that resemble fairy ring and enlarge each year. Clemson research found no insecticide affected them at three months. NC State’s advice is to keep the lawn vigorous and consider tolerant grasses; our lawn pest control guide covers the more common turf insects.
Frequently asked questions
How do you get rid of scale insects?
Identify armored or soft scale first, then time treatment to the crawler stage. Prune or scrub off heavy patches, spray horticultural oil in the dormant season or when crawlers are active, and use insecticidal soap on crawlers, repeating as the label allows. UC IPM recommends controlling ants and protecting natural enemies. On large trees, a systemic matched to the scale type may be warranted; follow the label.
Will Dawn dish soap kill scale?
It is not a reliable treatment. Iowa State Extension explains that dish soap is a detergent, not a true soap, that its effect on pests is limited and highly variable, and that it is much more likely to injure plants. Insecticidal soap is formulated for plants and kills crawlers on contact, but it will not reach adult scales under their covers, so repeated, well-timed applications are needed.
Are scale bugs harmful to humans?
No. Scale insects feed only on plant sap, and none of the extension sources we reviewed describe them biting people or carrying disease. Adults cannot move and crawlers are barely visible. The nuisance is indirect: soft scales drip sticky honeydew onto cars, patios and floors, sooty mould grows on it, and ants, wasps and yellowjackets gather to feed on the sugar.
What pesticide kills scale insects?
For most home gardens, extension sources favour horticultural oil, applied in the dormant season or at crawler time, and insecticidal soap on crawlers. Among systemics, UC IPM says dinotefuran controls most types of scale, while imidacloprid controls most soft scales but not most armored scales. UC IPM advises against broad-spectrum sprays such as carbaryl and pyrethroids, which kill natural enemies and can cause mite outbreaks.
Sources
- University of California Statewide IPM Program, Pest Notes: Scales, UC ANR Publication 7408.
- University of California Statewide IPM Program, Pest Notes: Mealybugs.
- University of Wisconsin Extension, Wisconsin Horticulture, Scale Insects.
- University of Maryland Extension, Introduction to Scale Insects.
- Penn State Extension, Magnolia Scale; and Crapemyrtle Bark Scale (updated 2025).
- Borden M, Martini X and Dale A, Crapemyrtle Bark Scale, UF/IFAS Extension EENY-711, 2018, reviewed 2022.
- Clemson Cooperative Extension, Home and Garden Information Center, Crapemyrtle Bark Scale.
- New Jersey Department of Agriculture, Division of Plant Industry, Horticultural Pests of Regulatory Concern Vol. III, Scale Insect Pests: Growing Degree Days for Crawler Stages.
- NC State Extension, Ground Pearls in Turf.
- Iowa State University Extension, Yard and Garden: Can I use dish soap instead of insecticidal soap?
- Missouri Botanical Garden, Scale (Indoors).
- The Pest Control Brief analysis of iNaturalist research-grade records, pulled October 2026.
