Curled pear leaves are almost always a problem of the new growth at the shoot tips, and the cause is usually an insect, not a disease. The way the leaf curls is the best clue. A leaf rolled tightly into a tube along its midrib, with red swellings, points to one pest, while a leaf cupped downward over a cluster of insects points to another. Wilted, blackened tips mean something more serious.

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The short answer: if young pear leaves are rolled tightly along the midrib, with red, gall-like swellings, the cause is the pear leafcurling midge. The leaves later turn black and fall (WSU Tree Fruit). It mainly matters on young trees. Leaves cupped and sticky with small insects underneath point to aphids or pear psylla. Shoot tips that wilt, blacken and bend into a hook are fire blight, which needs prompt pruning (The Morton Arboretum). Leaves that roll only in hot, dry weather are short of water.

Match the curl

What you see	Cause	When	How serious
Leaves rolled tight along the midrib, red swellings, tiny larvae inside	Pear leafcurling midge	Bloom to early summer	Low on mature trees, moderate on young trees
Leaves cupped or twisted, insects underneath, sticky honeydew	Aphids	Spring to early summer	Usually low
Sticky, sooty leaves on new growth; scorched-looking leaves	Pear psylla	Spring to summer	Moderate
Tips wilted, blackened, bent into a shepherd’s crook	Fire blight	Bloom to early summer	High
Leaves rolled or drooping in heat, no insects	Drought or heat	Summer	Depends on duration

Pear leafcurling midge

WSU Tree Fruit describes the pear leafcurling midge as a small fly of European origin. It was first found in New York in 1931 and has since spread to other pear-growing areas. It is a pest only of pears. Adults appear at bloom and lay eggs on young, still unfolded leaves. The larvae feed inside the leaf, which rolls tightly parallel to the midrib and develops red, gall-like swellings. A single leaf can hold up to 30 larvae. After about two weeks, they drop to the soil to pupate, and the curled leaves turn black and fall.

WSU notes that extensive feeding can stunt young trees but is of less concern on mature trees. It says the pest is not common and should not be a consideration in most pest management programs. Varieties differ: WSU lists Clapp’s Favorite, Red Bartlett and Alexander as very susceptible, and Anjou, Bosc and Bartlett as moderately susceptible.

What to do: on an established tree, pinch off and destroy curled leaves while larvae are still inside, then leave it. On a young tree that is being stunted, WSU says a spray at or shortly after petal fall can be considered. Leaves curled by the midge also shelter predators, such as ladybird beetles, that help control pear psylla.

Aphids

Aphids are soft-bodied insects that cluster on the undersides of new leaves and at shoot tips. The leaves cup, twist or curl downward. You will usually see the insects themselves, along with shed skins, sticky honeydew and ants. Aphid curling is looser and less tubular than midge damage, and the leaves stay green.

What to do: a strong spray of water knocks many off. Lady beetles and lacewings usually catch up within a few weeks. Avoid heavy nitrogen, which pushes the soft growth aphids prefer.

Pear psylla

WSU Hortsense describes pear psylla nymphs feeding on succulent new growth in the upper canopy. Damaged leaves may look blackened or burned. The nymphs produce large amounts of honeydew, which russets fruit and grows dark sooty mold. Heavy feeding reduces vigor and causes fruit loss.

What to do: WSU recommends encouraging natural enemies and avoiding broad-spectrum insecticides. Prune lightly, give moderate nitrogen and remove water sprouts and suckers. Kaolin clay, insecticidal soap or neem can be used as populations build. See pear leaves turning black for more on psylla and sooty mold.

Fire blight

Fire blight can look like curling at first, because infected young leaves wilt suddenly. The Morton Arboretum describes blossoms that turn brown and then black, and new growth that wilts and blackens. Infected shoot tips often bend into a hook. Utah State University Extension notes that pears are very susceptible and that removing infected wood is the best treatment.

What to do: cut out infected shoots at least 6 inches below visible damage, in dry weather, and sterilize your tools between cuts. Our guide to fire blight on pear trees covers this step by step.

Heat and drought

Pear leaves that roll or droop on hot afternoons and recover in the evening are short of water. The Morton Arboretum recommends checking the soil before watering: dig down an inch or two with a trowel, and water deeply only if it is dry. Young trees and trees in sandy soil are most at risk. Utah State also recommends keeping turf at least three feet from the trunk to reduce competition.

Diagnose in a minute

Unroll a curled leaf. Tiny orange or white maggots inside mean midge.
Turn over a cupped leaf. Clusters of insects mean aphids or psylla.
Look at the shoot tip. A blackened hook means fire blight.
Check the soil. Dry soil and no insects point to water stress.

If the leaves are spotted rather than curled, see pear leaf spots by color.

Sources

Pear Leafcurling Midge, WSU Tree Fruit, Washington State University
Pear: Pear Psylla, Washington State University Hortsense
Fire Blight, The Morton Arboretum
How to Grow Pears in Your Home Orchard, Utah State University Extension
Watering Trees and Shrubs, The Morton Arboretum

Top photo: Giancarlo Dessì, CC BY-SA 3.0, via Wikimedia Commons

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