Why Are My Pear Leaves Curling?

Pear leaf blister mite

Pear leaf blister mite (Eriophyes pyri) is a microscopic eriophyid mite that spends its entire lifecycle inside pear leaf tissue. The mites overwinter under the scales of pear buds and move into the developing leaves as they open in spring, where they feed within the cells and stimulate the formation of small, slightly raised blister galls. These blisters appear on the upper leaf surface as pale yellowish-green or pinkish patches, usually 2 to 5 millimetres across, often in large numbers across the leaf. Later in summer, as the mite population within the blisters dies, the blisters turn brown and then black, leaving the leaf with characteristic dark patches. The blistering causes some leaf puckering and distortion but rarely causes leaf drop or significant harm to an established tree.

What to do

• On small, young trees, or in severe infestations, apply a plant-based oil winter wash to the bark and buds in winter to smother overwintering mites and reduce the following year's population. There are no effective contact treatments once the mites are inside the leaf tissue.
• On established trees, pear leaf blister mite is primarily a cosmetic problem and does not need to be treated. The tree produces fruit normally even with heavy blistering. Accept it or apply a winter wash if the appearance is unacceptable.

Pear sucker

Pear sucker (Cacopsylla pyri) is a small psyllid insect that overwinters as an adult on the pear tree or in nearby bark and leaf litter. In spring, it moves to the buds and young leaves to feed and lay eggs. The nymphs feed on the sap of the leaves and young shoots, producing large amounts of honeydew that drips onto the foliage, shoots, and developing fruit below. The honeydew encourages the growth of sooty mould fungus, which coats the leaves and fruit in a black, sticky layer. Heavily infested trees have leaves that are yellowish, sticky, and covered in sooty mould; the fruit is also coated and its quality and appearance are significantly reduced.

What to do

• Apply a plant-based oil winter wash in December to January, before the buds swell, to smother overwintering adults and eggs on the bark.
• Encourage earwigs and other natural predators in the garden: earwigs are one of the most effective predators of pear sucker and populations are much lower in gardens where earwigs are present. Avoid broad-spectrum insecticides that kill natural enemies.
• In spring, apply insecticidal soap to the underside of leaves to target newly hatched nymphs. The nymphs are more vulnerable to contact treatments than the adults.

Pear scab

Pear scab (Venturia pirina) is a fungal disease that produces dark olive-green to black scabby spots on pear leaves, shoots, and fruit. On leaves, the spots may cause some puckering and distortion, and heavily infected leaves drop early. The disease overwinters in infected leaves and bark and spreads by spores in wet spring weather. It is one of the most common pear diseases in the UK.

What to do

• Rake up and destroy fallen leaves in autumn. Prune out infected shoots. Apply copper or sulphur fungicide from green cluster stage through to early summer in wet springs. Choose resistant varieties for new plantings: 'Conference' and 'Concorde' are less susceptible than older varieties.

Pear aphids

Pear-bedstraw aphid (Dysaphis pyri) and other pear aphids colonise shoot tips in spring, causing leaves to curl and pucker in a manner similar to rosy apple aphid on apples. Colonies on the underside of curled leaves are visible on close inspection. The damage is most significant on young trees.

What to do

• Inspect shoot tips from April. Treat emerging colonies before the leaves curl with insecticidal soap. Winter wash application in autumn smothers overwintering eggs.

Frequently asked questions

Why are my pear leaves blistering and curling?

Pear leaves blister and curl most commonly because of pear leaf blister mite (Eriophyes pyri) or pear sucker (Cacopsylla pyri). Pear leaf blister mite causes distinctive small, yellowish-green or reddish blisters on the upper surface of pear leaves, which appear in large numbers from late spring; the blisters turn black as the mites inside die in summer. These blisters do not usually cause severe leaf curling but do cause the leaves to pucker and distort. Pear sucker is a small, sap-sucking insect that colonises pear leaves and produces copious honeydew, causing sooty mould and leaf distortion. Pear aphids can also colonise shoot tips and cause leaf curling in spring.

What is pear leaf blister mite?

Pear leaf blister mite (Eriophyes pyri) is a microscopic eriophyid mite that lives inside pear leaf tissue, feeding within the cells and causing the leaf to produce blister-like galls. The mites are far too small to see with the naked eye. The blisters appear as small, slightly raised patches, initially yellowish-green or pale pink, on the upper surface of the leaf, often with corresponding depressions on the underside. As the summer progresses and the mites' lifecycle ends, the blisters turn brown and then black. In heavy infestations, the leaves may become extensively blistered and slightly puckered or curled, but rarely fall prematurely. The mite overwinters under bud scales and moves to the new leaves as they open in spring. Most established pear trees carry some level of pear leaf blister mite without significant harm; it is primarily a cosmetic problem on mature trees.

How do I control pear sucker?

Pear sucker (Cacopsylla pyri) is a small insect, somewhat similar to a psyllid, that causes leaves to yellow and distort and produces copious sticky honeydew that falls on the fruit and foliage below, encouraging sooty mould fungus. The presence of sooty mould on the upper surface of pear leaves and on the fruit is one of the most visible signs of a pear sucker infestation. Control: encourage natural predators (earwigs and other insects that prey on pear sucker populations) by avoiding broad-spectrum insecticides; apply a winter wash (plant-based oil spray) to the bark in winter to smother overwintering eggs; insecticidal soap applied to the undersides of leaves in spring targets the nymphs before they become adults. Pear sucker is most damaging in hot, dry summers; good canopy airflow and avoiding water stress reduce its impact.

Why do my pear leaves have black spots?

Black spots on pear leaves are most commonly caused by pear scab (Venturia pirina), a fungal disease that produces dark, olive-green to black, slightly raised spots or scabs on the leaves, fruit, and young shoots. It thrives in wet springs and is one of the most prevalent diseases of pear in the UK. The spots on leaves may cause the leaf to curl and distort, and in severe infections the leaves fall prematurely. Pear leaf blister mite blisters also turn black in summer, but these are raised blisters rather than flat spots. Control of pear scab: choose scab-resistant varieties when planting new trees ('Conference', 'Concorde', and 'Doyenne du Comice' are moderately resistant); rake up and destroy fallen leaves in autumn to remove the overwintering spore source; apply copper or sulphur fungicide from bud burst through to early summer in wet seasons; prune to maintain an open canopy with good airflow.