Euonymus scale
Euonymus scale is an armoured scale of euonymus, and UC IPM rates Japanese euonymus highly susceptible to it. Females are greyish-brown, oyster-shell shaped and about 1/16 inch (2 mm) long. Males are smaller, narrow and white, and often cover the stems so thickly that they look splashed with white. Feeding causes yellow spots on the leaves, then leaf drop, twig dieback and, if it goes unchecked, the death of the plant. There are two generations a year, and each has a crawler stage that oil or soap can kill: late April to May, then late July into early September. Japanese euonymus is the most susceptible. On a plant that keeps getting reinfested, replacing it with a tolerant species is the lasting fix.
Unaspis euonymi males and females crowded on a euonymus stem. Photo: pending.
Identification
Females live under a greyish-brown, flattened, pear- or oyster-shaped waxy cover about 2 mm (1/16 in) long. Males live under narrow white covers about 0.8 mm long, and are what gives heavily infested stems their white-flecked look. Crawlers are yellowish-orange and about 0.3 mm long.
As an armoured scale, it produces no honeydew and no sooty mould, which separates it from soft scales. The cover lifts off, and the soft body underneath stays on the plant.
Easily confused with
- Parasitised scaleBeneficial — leave itA round exit hole in the scale's back, or a scale gone puffy or darker than its neighbours, means a parasitic wasp has already killed it. Leave it be.
- Cottony camellia scaleAlso a pestAlso found on euonymus, but its yellow-tan female cover carries a white cottony egg sac about 1/4 inch (6 mm) long; euonymus scale shows narrow white male covers and brown, pear-shaped females.
Damage symptoms
Euonymus scale sucks sap from stems and leaves. Penn State describes yellowish stippling or spotting of the foliage, and heavy infestations cause leaf drop, twig dieback and plant death. Kentucky adds that affected plants look water-stressed and thin. Vine-type euonymus is extremely susceptible, according to Penn State.
- Yellow spots or stippling on the leaves
- Stems and leaf undersides flecked with white male scales
- Plants that look thin and water-stressed
- Leaf drop and dying twigs, sometimes whole plants
Lifecycle & degree days
Mated females overwinter on the stems and lay eggs under their covers from late April. In Kentucky, first-generation crawlers emerge over about two weeks from late April to early May and are active until late May. They mature in four to six weeks, and second-generation crawlers are active from late July into early September. Penn State gives the same pattern for Pennsylvania. Dates shift with the season and the region, so confirm crawler timing with tape.
- Generations / yr
- 2 (Pennsylvania, Kentucky)
- 1st crawlers
- Late April–May
- 2nd crawlers
- Late July–early September
- Overwinters
- Mated females on stems
Host crops
Euonymus is the main host, and the species differ a great deal. UC IPM rates Euonymus japonicus highly susceptible, E. kiautschovicus tolerant and winged euonymus (E. alatus, burning bush) unaffected. Penn State adds pachysandra and bittersweet. Kentucky lists burning bush, English ivy, holly, honeysuckle and lilac among common hosts, which contradicts UC on burning bush. In practice, evergreen and vining euonymus are where the damage is.
Monitoring & action thresholds
No numeric threshold is published. Because the scale can kill plants, act on the first infested stems: prune them out, then time a crawler spray for the next generation.
Check stems and leaf undersides from spring, and look hardest at plants with yellow-spotted leaves. To time a spray, wrap double-sided sticky tape round infested stems in spring before the crawlers emerge (they appear from late April in Kentucky), and change it weekly. The yellow-orange crawlers stick to it. UC IPM's general advice is to spray once crawler numbers have peaked and begun to fall. Repeat the watch before late July for the second generation.
Biological control
The lady beetle Chilocorus kuwanae is black with two red spots and about 3–5 mm long (Penn State gives 3–4.5 mm, UC IPM 4–5 mm). The USDA imported it several times from China, Korea and Pakistan, and Penn State says it was introduced in the eastern US to help manage euonymus scale. It is now established in much of the US. UC IPM notes that each larva eats more than 100 scales. The native twicestabbed lady beetle, Chilocorus orbus, and the small Rhyzobius lady beetles also feed on armoured scales, and parasitic wasps such as Aphytis and Encarsia attack them too. Treat them as wild allies to conserve rather than something to buy: use oil rather than broad-spectrum sprays.
Cultural controls
Pruning, crawler timing and plant choice do more than any product.
- Prune out and destroy heavily infested stems and twigs
- Spray horticultural oil or insecticidal soap on the crawlers: late April–June for the first generation, late July–early September for the second
- Oil rates on one residential label (Bonide, EPA Reg. 4-80, shrubs and broadleaf evergreens): 5–7.5 tbsp per gallon dormant, 2–5 tbsp per gallon in summer. Follow your own label. The oil is toxic to fish, so keep it out of drains and water, and keep people and pets off until the spray dries
- Do not spray oil below 40 °F or above 90 °F, or on plants under drought stress
- Wet the stems and leaf undersides thoroughly, because oil only kills what it touches
- Water in dry spells and follow a sensible feeding programme, but do not over-fertilise, which Kentucky says favours scale build-up
- Replace repeatedly infested Japanese euonymus with a tolerant species such as E. kiautschovicus, or with a non-host
Chemical, last resort
- Horticultural oilREI 12 h
Sources
Penn State Extension, Euonymus Scale (G.A. Hoover, rev. 2003)
Univ. of Kentucky ENTFACT-428, Euonymus Scale (Larson & Townsend, rev. 3/26)
UC IPM Pest Notes 7408, Scales (Kabashima & Dreistadt, 2014)
UC IPM Natural Enemies Gallery, Chilocorus kuwanae lady beetle
UC IPM Natural Enemies Gallery, Rhyzobius lady beetles
Bonide Horticultural & Dormant Spray Oil label, EPA Reg. 4-80 (2024)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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