Why Are My Cherry Leaves Curling?

Cherry blackfly

Cherry blackfly (Myzus cerasi) is a distinctive, jet-black aphid that is one of the most recognisable pest symptoms on UK garden trees. Overwintering eggs hatch from bud burst in April, and the aphids rapidly colonise the growing tips of cherry shoots in dense, black masses. The young leaves at the growing tip curl tightly inward around the aphid colonies, and the shoot becomes stunted and misshapen. The sheer density of the black aphid mass on curled cherry shoot tips is striking and alarming; it is the most common reason that cherry growers contact garden advisers in spring.

By midsummer, most colonies naturally migrate to their summer host plants (bedstraws, Galium species, and related plants) and leave the cherry tree. The plant's later growth, produced after the aphid migration, is clean and undamaged. On established trees, cherry blackfly is a recurring annual problem that is largely cosmetic unless the infestation is so severe that the whole canopy of growing tips is affected.

What to do

• The only effective control window is spring, from bud burst in April, before the leaves have curled around the aphids. Inspect the growing tips as they emerge and treat colonies at this stage with insecticidal soap, pyrethrum, or a plant oil spray, covering all surfaces thoroughly.
• Once the leaves have curled tightly around the aphid colony (typically by May), contact insecticides cannot penetrate to the insects inside. At this stage, pinch out and destroy the most heavily infested shoot tips if the tree is small enough; on large trees, accept the cosmetic damage and wait for the aphids to migrate naturally in July.
• In autumn, apply a winter wash (plant-based oil spray) to the bare branches to smother overwintering eggs and reduce the following year's population.
• Allow natural predators to establish: avoid insecticide use in early spring that kills ladybirds and hoverflies. Colonies that survive into June are quickly parasitised and predated.

Powdery mildew

Cherry powdery mildew (Podosphaera clandestina) produces a white, powdery coating on the young leaves in spring and early summer, causing them to curl and distort. It overwinters in infected buds and re-infects new growth in spring. Mildew is most common on cherry trees in dry summers when there is a combination of dry roots and humid air.

What to do

• Remove and destroy mildewed shoots in spring. Improve airflow by pruning to maintain an open crown. Water the soil during dry spells (not the foliage). Apply sulphur-based fungicide from bud burst for trees with persistent annual mildew.

Leaf scorch

Cherry bacterial canker (Pseudomonas syringae pv. morsprunorum) causes shot hole symptoms and brown patches on leaves rather than curling, but associated twig death and the stress it causes can make surrounding leaves curl and yellow. It enters through leaf scars in autumn and is favoured by wet autumn weather. Pruning wounds and frost damage provide additional entry points.

What to do

• Prune cherry only in May to August to minimise the risk of bacterial canker infection. Remove and destroy cankered branches, cutting to clean wood well below the visible canker.

Drought

Drought causes cherry leaves to curl upward at the margins, develop a dull sheen, and drop prematurely. Young, recently planted cherry trees are particularly susceptible in their first two to three summers before the root system is fully established. Water stress during fruit development reduces berry size and causes split fruit in some varieties.

What to do

• Water newly planted cherry trees regularly through their first two to three summers, particularly during dry spells and during fruit development. Mulch generously around the base to retain soil moisture. Established trees on deep soils rarely need irrigation except in exceptional drought years.

Frequently asked questions

Why are my cherry leaves curling?

Cherry leaves curl most commonly because of cherry blackfly (Myzus cerasi) or powdery mildew (Podosphaera clandestina). Cherry blackfly is the most visually striking cherry pest: dense, jet-black aphid colonies colonise the growing tips of cherry shoots from late April, causing the leaves to curl tightly inward around the insects, the shoots to become distorted and stunted, and the entire growing tip to appear black with the aphid mass. Powdery mildew produces a white, powdery coating on young leaves, causing them to curl and distort. In both cases the damage is most severe on young, soft growth; established, mature cherry trees tolerate these problems better than young, recently planted trees.

What is cherry blackfly and how do I control it?

Cherry blackfly (Myzus cerasi) is a small, jet-black aphid that is one of the most easily recognised garden pests in the UK. It overwinters as eggs on cherry bark and hatches from the bud burst stage in April or May. The aphids colonise the growing tips in large, dense, black masses that cover the young leaves and stems. The leaves at the growing tip curl tightly inward around the aphid colonies, and the shoot becomes stunted and distorted. By midsummer, most colonies migrate to their summer hosts (bedstraws and other plants) and the cherry tree's remaining growth is undamaged. Control: the effective control window is spring, before the leaves have curled tightly around the aphids. From bud burst in April, inspect the growing tips and treat emerging colonies with insecticidal soap, pyrethrum, or a plant oil spray. Once the leaves are tightly curled around the aphids, contact sprays cannot penetrate the curled tissue. Natural predators (ladybirds, hoverfly larvae) provide useful control from June onward.

Does cherry blackfly affect the fruit?

Cherry blackfly primarily affects the growing tips and young leaves rather than the fruit directly. However, severely infested shoots produce stunted, distorted growth and the leaves on affected shoots provide less photosynthetic support to the tree, which can reduce fruit size and quality in a very heavy infestation year. The cherry fruit itself is not colonised by the blackfly and is safe to eat, though heavily infested small trees may produce a reduced crop. On established, large cherry trees, cherry blackfly is largely a cosmetic problem: the tree has enough mature, unaffected foliage to compensate for the infested shoot tips, and the infestation naturally declines as the aphids migrate in midsummer. Most home gardeners with established cherry trees find that cherry blackfly is a recurring annual annoyance rather than a serious threat to the harvest.

How do I prevent silver leaf disease on cherry?

Silver leaf disease (Chondrostereum purpureum) is a serious fungal disease of cherry and other Prunus trees that does not cause leaf curling but does cause the leaves to develop a distinctive silvery, metallic sheen. It enters the tree through pruning wounds and damaged bark. The most important prevention measure is to prune cherries only in late May to August when the tree is actively growing and the spores of the silver leaf fungus are less prevalent in the air and the tree's wound-healing is fastest. Never prune cherry in autumn, winter, or early spring. Use sharp, sterilised tools and make clean cuts that heal rapidly. Paint large wounds with a wound sealant if desired, though modern guidance suggests this is not strictly necessary if cuts are clean. If silver leaf is confirmed (by cutting an affected branch: the wood inside shows a dark brown stain), remove the infected branch to at least 10 centimetres beyond the last sign of internal staining.