Cornus Leaves Curling

Aphids

Aphids are the most common pest on cornus and a frequent cause of curling, distorted leaves. Several species colonise dogwood: the dogwood aphid forms dense colonies on young shoot tips and leaf undersides, while woolly aphids produce a white waxy coating on older stems. On actively growing spring shoots, the youngest leaves curl tightly around the colonies, making the insects difficult to see without carefully unrolling the affected foliage. Honeydew excreted by the aphids coats nearby leaves and may encourage sooty mould. In summer, winged forms spread the infestation through the plant. Shrubby cornus grown for coloured winter stems (C. alba, C. sericea, C. sanguinea) are all affected, as are flowering dogwoods.

Treat aphids on cornus early before colonies become established across multiple shoot tips. A strong blast of water from a hose dislodges most insects and is highly effective on shrubs. Follow up with an insecticidal soap spray applied to all affected shoot tips and the undersides of curled leaves. For severe infestations on larger shrubs or trees, a systemic insecticide may be needed, but avoid it if the cornus is in a position where it is visited by pollinators or if it is near a pond or watercourse. Natural predators, particularly ladybirds and their larvae, work through cornus aphid colonies effectively once the season is underway and colonies rarely persist beyond early summer without intervention.

Powdery mildew

Powdery mildew is one of the most common fungal problems on cornus and particularly affects the flowering dogwoods (Cornus florida, C. kousa, and their hybrids). The disease appears as a white or grey floury coating on the upper surface of leaves, starting typically on the lower branches where air movement is poorest. Affected leaves curl at the margins and may pucker or distort. In severe cases the upper canopy is affected and leaves drop early, reducing the plant's autumn colour display and potentially weakening the shrub over successive seasons. Shrubby dogwoods grown for their winter stems are generally less susceptible than the flowering forms.

Prune cornus to open up the centre of the plant and improve air circulation through the canopy. Avoid overhead irrigation which wets the foliage in conditions that favour fungal spread. Remove and bin affected leaves and small twigs promptly. Spray affected plants with a potassium bicarbonate fungicide or a copper-based spray at the first sign of the white coating, and repeat at ten-day intervals. Some Cornus kousa cultivars, including 'Satomi' and 'Milky Way', show better mildew resistance than C. florida types and are worth considering for gardens where mildew is a persistent problem.

Drought

Cornus grown for winter stem colour (the shrubby dogwoods) are more drought-tolerant than the flowering tree forms, but young plants of all cornus types can suffer drought stress, particularly in their first two to three years before their root systems are established. Drought causes leaves to curl inward along their midrib, with edges often turning brown. The curling is most pronounced during afternoon heat. Unlike aphid damage, which is concentrated on the youngest leaves at shoot tips, drought affects leaves across the whole plant more uniformly, starting with the outer canopy where sun exposure is greatest.

Water newly planted cornus regularly during dry spells in their first two growing seasons. Apply a generous mulch of bark chippings around the root zone, extending out to the drip line of the canopy, to reduce evaporation and keep soil temperatures lower. Flowering dogwoods (C. kousa and C. florida) prefer reliably moist, well-draining soil and are less drought-tolerant than many other trees once fully established. In warm climates or on light, sandy soils these trees benefit from supplementary watering throughout their lives, particularly during bud formation in late winter and spring.

Leaf scorch

Leaf scorch is a common problem on Cornus kousa and flowering dogwoods planted in full sun or against a south- or west-facing wall. The large, thin leaves heat up rapidly in direct sunshine and lose moisture faster than the roots can supply, causing the leaf margins to brown and curl upward. Scorch damage on cornus has a distinctive pattern: brown, papery margins sharply defined from the green interior, with the leaf curled toward the scorched surface. It is most common during hot, dry summers and on plants growing in exposed positions without shelter from neighbouring trees or structures.

Cornus kousa and its cultivars perform best in dappled shade or in a position sheltered from the hottest afternoon sun. If scorch is a recurring problem on an established plant, increase watering frequency during hot spells to reduce moisture deficit in the leaves. A temporary shade cloth erected on the south side of the plant during heat waves reduces scorch significantly. Mulching the root zone to retain soil moisture is particularly important for flowering dogwoods in sunny positions. Note that minor marginal scorch on otherwise healthy cornus rarely causes lasting damage and the plant typically recovers fully the following season.

Caterpillars

Several caterpillar species feed on cornus leaves in spring and early summer. Winter moth caterpillars are among the most damaging: they emerge in spring to coincide with budburst and feed on the expanding leaves, spinning silk threads that cause the leaves to roll and stick together in tight clusters. This distinctive rolled, tied appearance is unlike the uniform curling caused by drought or mildew. Other caterpillar species eat holes through the leaf tissue without the silk tying, and the damaged leaf curls around the wound as it continues to grow. Heavy caterpillar pressure on young cornus can cause significant defoliation.

Check cornus in early spring for the silken webbing and small green or brown caterpillars characteristic of winter moth damage. Remove individual rolled leaves by hand on small shrubs or young trees. For larger infestations, spray with an appropriate caterpillar treatment such as a Bacillus thuringiensis (Bt) biological spray, which is effective on moth and butterfly caterpillars without harming most beneficial insects. Apply in the cool of evening when caterpillars are actively feeding. Grease band traps applied to the trunk in autumn prevent the wingless adult female winter moths from climbing up to lay eggs.

Leaf spot

Leaf spot diseases, including anthracnose and several fungal spot pathogens, affect cornus and can cause leaf distortion alongside the characteristic brown or purple spots. Anthracnose of dogwood (caused by Discula destructiva) is particularly serious on Cornus florida in damp, cool conditions, and leads to leaf spots, stem dieback, and leaf curling as the fungus spreads through the tissue. The spots begin as small water-soaked areas and expand into larger tan or brown blotches with purple margins. Severely affected leaves curl, brown, and drop early.

Improve air circulation around cornus by pruning out congested growth and removing dead or diseased branches to clean wood. Rake up and bin fallen leaves promptly, as spores overwinter in leaf debris and reinfect the plant the following spring. Apply a copper-based fungicide or a dedicated anthracnose spray at budbreak in spring before symptoms appear, as a preventive measure in gardens where the disease has occurred previously. Cornus kousa and its cultivars have notably better resistance to anthracnose than C. florida and are strongly recommended in areas where the disease is endemic.

Frequently asked questions

Why are my cornus leaves curling?

Aphids and powdery mildew are the most common reasons cornus leaves curl. Check the undersides of young leaves for colonies of soft-bodied insects and look for a white floury coating on the leaf surface. Drought and leaf scorch from strong sun can also cause cornus leaves to curl.

Does dogwood get powdery mildew?

Yes, many cornus species are susceptible to powdery mildew, particularly Cornus florida and its hybrids. The disease appears as a white coating on leaves, causing them to curl and distort. Improve air circulation and spray with a potassium bicarbonate fungicide at the first sign of infection.

Why are my dogwood leaves curling and turning yellow?

Curling combined with yellowing on cornus can indicate aphids, root problems, or drought stress. Check the undersides of leaves for pests, then inspect the soil moisture level. Yellowing from the leaf edges inward without pests often points to drought or nutrient deficiency.

What is eating my cornus leaves?

Several insects feed on cornus leaves. Aphids cluster on undersides and cause curling. Sawfly larvae eat through leaf tissue leaving ragged holes and the leaf may curl around them. Winter moth caterpillars feed in spring on young leaves, causing them to curl and tie together with silk threads.