Why Are My Pear Tree Leaves Distorted and Sticky?

Sticky, distorted leaves on a pear tree in spring or early summer are a reliable sign of aphid infestation. Several species of aphid feed on pear trees, and while small colonies do little lasting harm, large populations can badly distort young growth, coat leaves and fruit in honeydew, and attract sooty mould that reduces the tree's ability to photosynthesise effectively.

Identifying pear aphid species

Several species attack pear trees. The pear-grass aphid (Sitobion fragariae) and Dysaphis pyri both cause tightly curled, distorted young leaves in spring. Colonies are often found trapped inside the curled leaf. The pear bedstraw aphid moves to secondary host plants by midsummer, and infestations on the tree often collapse naturally by July. Check the undersides of curled or distorted leaves carefully — the insects are small, soft-bodied, and range from pale green to yellowish or pinkish depending on species.

Honeydew and sooty mould

Aphids excrete large quantities of sticky honeydew as they feed. This coats leaves, shoots and sometimes developing fruit below the infestation, creating an ideal surface for the growth of black sooty mould. Sooty mould does not directly infect plant tissue but blocks light from reaching the leaf surface and reduces photosynthesis. Heavy mould deposits can be washed off with water. Controlling the aphids eliminates the honeydew source and sooty mould disappears within a season.

Encouraging natural predators

Ladybird adults and larvae, lacewing larvae, hoverfly larvae, parasitic wasps and birds all feed heavily on aphids. Avoiding broad-spectrum insecticide sprays — which kill these predators along with the pest — is the single most important step in keeping aphid numbers manageable. Planting flowering perennials around the base of the tree (borage, phacelia, umbellifers) provides nectar and pollen that maintain predator populations early in the season.

Direct treatment of heavy infestations

If a colony is causing severe distortion on a small or young tree, a targeted spray of insecticidal soap solution directly onto the colonies — making sure to reach the undersides of curled leaves — kills aphids on contact without persisting in the environment. Apply in the early morning or evening when beneficial insects are less active. Repeat after 5–7 days if the colony re-establishes. On accessible branches, simply squashing colonies by hand is highly effective.