Why Are My Pear Tree Leaves Curling?

Pear tree leaves that curl, pucker or distort are almost always responding to something feeding on them or growing inside them. The curling is rarely a disease in itself but a symptom — the leaf's response to sap-sucking insects, mites or fungal infection. Identifying the culprit correctly is the key step, because treatments differ significantly between an aphid infestation and a mite problem.

Pear aphids — sticky curling in spring

Several species of aphid attack pear trees, most noticeably in spring when soft new growth is most vulnerable. Rosy apple-grass aphid and pear-grass aphid both cause young leaves to curl tightly inward, often trapping the aphids inside the roll. Check the undersides of affected leaves and the growing tips — you will find colonies of small green or yellowish insects. Sticky honeydew dripping from infested leaves is another clear sign. On small trees, squash colonies by hand or spray with an insecticidal soap solution. Encourage natural predators such as ladybirds, lacewings and blue tits by avoiding broad-spectrum pesticides.

Pear leaf blister mite — blistered puckering

Pear leaf blister mite (Eriophyes pyri) causes raised blisters and puckering rather than classic rolling. Affected areas start pale green or yellow-green, later turning pink and then brown as the season progresses. The mites live inside the leaf tissue, making them invisible to the naked eye but identifiable by the pattern of damage. Severe infestations cause premature leaf drop and can affect fruit finish. There are no approved acaricides available to home growers for this pest in most countries. Winter tar-oil washes, where permitted, reduce mite populations overwintering in bark. Removing and destroying heavily infested leaves slows spread.

Pear psylla — curling with heavy honeydew

Pear psylla (Cacopsylla pyri) nymphs are small, flat, pale insects that feed on leaf sap and excrete enormous quantities of sticky honeydew. Infested leaves curl and become coated in honeydew, which then attracts sooty mould, turning the foliage black. Psylla are most problematic in warm, dry seasons. Predatory insects keep populations in check in organic gardens, but heavy infestations may warrant targeted insecticidal soap sprays, applied thoroughly to reach the nymphs on the leaf undersides.

Powdery mildew on young shoots

Young pear shoots infected with powdery mildew produce leaves that emerge crinkled, narrow and cupped, often with a faint white powdery coating. The distortion is caused by the fungus colonising the leaf tissue before it has fully expanded. Prune out affected shoot tips as soon as you notice them in spring — they carry the overwintering spores of the fungus and will reinfect new growth if left in place. Improving air circulation through the canopy with annual pruning reduces the conditions that favour mildew.