Euonymus Leaves Curling
Euonymus scale and powdery mildew are the most common reasons euonymus leaves curl. This guide shows you how to identify each cause and keep spindle plants healthy and attractive.
1. Euonymus scale (Unaspis euonymi)
Euonymus scale is an armoured scale insect that is among the most serious pests of euonymus, particularly Euonymus japonicus and its cultivars. It is established in many parts of southern England and its range is expanding northward. Heavy infestations can cause significant dieback and are one of the primary reasons euonymus hedges become thin, unhealthy, and unattractive.
What to look for
White elongated scale covers (males) appear as streaks on stems and branches, giving the bark a whitewashed or frosted appearance. The brownish, oyster-shaped female covers are found on the undersides of leaves and on bark. Heavily infested leaves turn yellow, develop small pale spots where individual scale are attached, and curl or drop early. Stems become encrusted and die back progressively from the tips in severe infestations. Sooty mould on honeydew deposits may also be present.
What to do
Apply a horticultural oil (white oil or tar wash) to all stems in late winter or early spring before bud burst, smothering the overwintering scale under their shells. In late May through June, when the mobile first-instar crawlers are active, spray the whole plant thoroughly with horticultural soap at ten-day intervals for six weeks; the crawlers are killed easily but the armoured adults are not. Scrub accessible bark with a stiff brush dipped in soapy water to physically dislodge dense colonies. On badly infested plants, hard pruning in late winter removes the most heavily infested wood and allows you to treat regrowth cleanly. Replace Euonymus japonicus with the more scale-resistant E. fortunei in gardens where scale is a persistent problem.
2. Powdery mildew (Oidium euonymi-japonici)
A specific powdery mildew fungus, Oidium euonymi-japonici, affects euonymus and is particularly common on Euonymus japonicus and its cultivars. It is encouraged by warm, dry days and cool, humid nights, and spreads rapidly through the canopy of plants grown in sheltered or enclosed positions where air circulation is limited.
What to look for
A white or pale grey powdery coating appears on the upper surface of leaves, particularly on young growth. Affected leaves curl upward and inward and may appear puckered or distorted. On variegated cultivars the mildew is most obvious on the green portions of the leaf. Severely infected shoots may fail to elongate normally. In heavy infections the whole plant takes on a greyish, unhealthy appearance and may lose ornamental appeal.
What to do
Improve air circulation by thinning the plant and removing congested stems. Avoid planting euonymus in enclosed, sheltered positions where air movement is minimal. Remove and bin heavily infected shoots. Spray with diluted milk solution (one part whole milk to nine parts water) every two weeks from the first signs of infection. A sulphur-based or myclobutanil-based fungicide provides stronger control for persistently affected plants. Avoid high-nitrogen feeding in late summer as this encourages the soft new growth that is most susceptible.
3. Euonymus ermine moth (Yponomeuta cagnagella)
The euonymus ermine moth is a specialist caterpillar that feeds communally on euonymus, spinning a dense silky web around the plant as it feeds. Infestations are dramatic in appearance and can cause complete defoliation, but healthy established plants almost always recover and refoliate once the caterpillars have gone.
What to look for
Sheets of fine silky white webbing appear over the stems and foliage of euonymus from late spring through midsummer, draped over whole sections of the plant or hedge. Inside the webbing, dozens to hundreds of small (up to 15 mm) pale caterpillars with rows of black dots feed on the leaves, reducing them to bare stems. After pupation in midsummer, the webbing persists for a time but the caterpillars are gone. New foliage typically flushes from the bare stems through late summer.
What to do
On small plants or young infestations, remove sections of webbing by hand while wearing gloves and bin them along with the caterpillars inside. For larger infestations on hedges or established shrubs, the most practical approach is to wait: the caterpillars pupate and leave by midsummer, and the plant refoliates. If intervention is necessary, a biological insecticide based on Bacillus thuringiensis (Bt) applied to the caterpillars inside the web as early as possible in the infestation is effective and safe for beneficial insects. Avoid broad-spectrum insecticides which kill natural parasitoid wasps that provide long-term control of ermine moth populations.
4. Vine weevil (Otiorhynchus sulcatus)
Euonymus, particularly container-grown specimens, is a favoured host of vine weevil. The adult beetles notch the leaf margins while feeding at night, and the larvae feed on roots in the compost, causing potentially fatal root damage. Container plants are at much greater risk than those in the open ground.
What to look for
Irregular notches cut from the margins of leaves are made by adult beetles feeding at night. While the notching is unsightly, it is rarely severe enough alone to seriously harm the plant. More serious is root damage by larvae: the plant wilts and leaves curl despite adequate watering, as the root system has been destroyed. If you tip a container plant out of its pot, white C-shaped grubs among the roots confirm vine weevil. In the ground, wilting without obvious cause in an otherwise healthy plant warrants investigation of the roots.
What to do
Apply parasitic nematodes (Steinernema kraussei) to compost or soil in late summer and early autumn when soil temperature is between 5 and 20 Celsius, for effective biological control of larvae. For container plants, replace infested compost and treat the new compost with nematodes before repotting. Collect adult beetles at night using a torch; they hide in soil, leaf litter, and under pots during the day. Sticky barriers around pot rims can prevent adults from climbing in to lay eggs. Check new container plants from garden centres carefully, as vine weevil larvae are often introduced on new purchases.
5. Drought stress
Euonymus is generally tolerant of dry conditions once established in the ground, but container plants and E. fortunei in exposed, windy positions can suffer drought stress during hot summers. Drought causes leaf curl and marginal scorch, and weakens the plant's resistance to other problems, particularly scale insects and mildew.
What to look for
Leaves curl inward and the foliage may lose some of its colour brilliance on variegated cultivars. In more severe drought the leaf margins and tips turn brown, beginning with the oldest leaves. Container plants may wilt visibly within a day or two of hot weather if not watered. E. fortunei in exposed, windy sites can show winter desiccation, where leaves brown and curl in cold, drying winds even when air temperature is not below freezing.
What to do
Water container euonymus thoroughly every day or two during warm weather, ensuring water drains freely from the pot. Stand pots on feet to maintain drainage. For wall-trained or exposed garden plants suffering from winter desiccation, apply an anti-desiccant spray to the foliage in late autumn and move container plants to a sheltered position. Mulch the root zone of garden plants with a 75 to 100 mm layer of wood chip to conserve moisture and moderate soil temperature through summer. Feed annually in spring with a balanced slow-release fertiliser to maintain vigour.
Frequently asked questions
Why does my euonymus have white streaks on the stems?
White streaks or encrustation on euonymus stems are caused by euonymus scale (Unaspis euonymi), an armoured scale insect. The white elongated covers belong to the male scale; the brownish oyster-shaped covers are female. Heavy infestations cause yellowing, leaf curl, and dieback. Treat with horticultural oil in late winter and soap spray when crawlers are active in late spring.
Why is my euonymus hedge covered in white webbing?
Silky white webbing covering stems and defoliating euonymus is the work of euonymus ermine moth caterpillars (Yponomeuta cagnagella). Colonies of small pale caterpillars feed communally inside the web tent, stripping the plant of its leaves. The plant usually recovers and refoliates once the caterpillars have pupated in midsummer; no treatment is strictly necessary for healthy plants.
How do I treat euonymus scale?
Apply a plant-based white oil or tar oil wash to dormant wood in late winter to smother overwintering scale. In late May and June when mobile crawlers are active, spray with horticultural soap at ten-day intervals for six weeks. Scrub accessible bark with a stiff brush and soapy water to physically remove dense colonies. Natural predators including parasitic wasps help control populations; avoid broad-spectrum insecticides.
Why is my euonymus japonicus losing its variegation?
Loss of variegation (reverting to plain green) on euonymus japonicus cultivars is caused by shoots reverting to the non-variegated form. This is a genetic reversion, not a disease. Remove all-green shoots immediately by cutting back to the main stem, as the reverted growth is more vigorous and will quickly overtake the variegated portions if left.
Is euonymus poisonous?
Yes, all parts of euonymus plants are toxic if ingested, particularly the berries and seeds, which contain alkaloids and cardiac glycosides. Keep children and pets away from the berries. Contact with the sap can cause skin irritation in sensitive individuals. Always wash hands after handling euonymus, especially when pruning.
Find the best spot for your plants
Plant Compass maps the sun path across your windows so you know exactly which plants will thrive in each spot before you buy. Coming soon to the App Store.
Learn more