Plant problems

Why Are My Crabapple Leaves Curling?

Q: Why are my crabapple leaves curling?

Crabapple (Malus species and cultivars) leaves curl most commonly in the UK because of rosy apple aphid (Dysaphis plantaginea), apple powdery mildew (Podosphaera leucotricha), or apple capsid bug (Plesiocoris rugicollis). The rosy apple aphid is the most characteristic cause of severe leaf curl on crabapple: colonies of small, pink-brown aphids build up on the undersides of the young leaves from bud burst in April, causing the leaves to curl tightly downward and inward, often turning purplish-pink; the curled leaves are persistent and the distortion remains even after the aphids leave in summer. Apple powdery mildew produces a white, powdery coating on the young shoot tips and leaves; affected shoot tips are stunted and the leaves fail to expand fully, producing a distinctive silvery-white rosette of curled, distorted leaves at the shoot apex. Apple capsid bug feeding on the young leaves in spring produces small holes and scarring that can cause leaf distortion and curling as the damaged tissue fails to expand normally. Apple scab (Venturia inaequalis) causes dark, scabby spots on the leaves followed by yellowing, curling, and premature drop; scab is especially damaging on susceptible crabapple varieties in wet springs.

Q: What are the best crabapples for UK gardens?

Crabapples (Malus species and cultivars) are among the most versatile small trees for UK gardens, offering spring blossom, attractive summer foliage, autumn fruit, and winter fruit display (the fruits often persist on the tree through winter, providing food for birds). The most popular UK garden crabapples include: Malus 'John Downie' (perhaps the most popular fruiting crabapple; large, conical orange-red fruit excellent for jelly; white blossom), Malus 'Golden Hornet' (abundant small, bright yellow fruit that persist well into winter; white blossom), Malus x robusta 'Red Sentinel' (dark red fruit that persists until February; excellent disease resistance), Malus floribunda (Japanese flowering crabapple; masses of deep pink buds opening to pale pink or white flowers; small, yellow-red fruit; excellent disease resistance), Malus 'Evereste' (dark pink buds opening to white flowers; orange-red fruit; very disease-resistant; one of the best all-round choices), Malus 'Laura' (deep red-purple foliage; pink flowers; dark red fruit; ornamental but less disease-resistant). For fruit-making (crabapple jelly), 'John Downie' is the standard recommendation; for combined ornamental and wildlife value, 'Red Sentinel', 'Evereste', and 'Golden Hornet' are excellent. Choosing a disease-resistant variety significantly reduces problems with apple scab, mildew, and fireblight.

Q: How do I make crabapple jelly?

Crabapple jelly is one of the easiest fruit jellies to make because crabapples are very high in pectin (which sets the jelly naturally) and acid (which gives the jelly its flavour and helps it set), so no added pectin is needed. The method is as follows: wash the crabapples (no need to core or peel; the seeds, cores, and skins all contribute pectin) and cut off any bruised areas. Place in a large pan and add enough water to just cover the fruit; bring to the boil and simmer until the fruit is completely soft and pulpy, about 30 to 45 minutes. Pour the pulp into a jelly bag (or a muslin-lined colander) over a large bowl and leave to drip overnight; do not squeeze the bag, as this makes the jelly cloudy. Measure the liquid and add 450g of sugar per 600ml of juice. Dissolve the sugar in the juice over low heat, then bring to a rolling boil and boil hard until setting point is reached (104°C on a sugar thermometer, or when a small drop of jelly on a cold plate wrinkles when pushed). Skim off foam, pour into sterilised jars, and seal immediately. The resulting jelly should be clear amber-pink to deep red (colour depends on variety); it is excellent with game, pork, lamb, cheese, and as a glaze for pork or duck.

Q: How do I control rosy apple aphid on crabapple?

Rosy apple aphid (Dysaphis plantaginea) is one of the most damaging aphids on crabapple because the curled, distorted leaves it produces persist through the summer even after the aphids have left; control must be applied early, before the leaves curl tightly around the colonies. To control: inspect the undersides of the young leaves from bud burst (April) and apply insecticidal soap, neem oil, or pyrethrin spray immediately when colonies are first detected; once the leaves have curled tightly around the aphid colony, sprays cannot reach the insects inside the roll. Apply a winter oil wash to the dormant bark in December to January; this smothers overwintering rosy apple aphid eggs on the bark and significantly reduces the following spring's infestation. Encouraging natural predators (ladybirds, lacewings, hoverfly larvae) by planting nectar-rich flowers near the crabapple provides ongoing biological control. Note that rosy apple aphid migrates to plantain (Plantago species) as its summer host; removing plantains from the vicinity of the crabapple will reduce re-colonisation the following spring.

Crabapple (Malus species and cultivars) is one of the most popular small trees for UK gardens, offering a spectacular spring blossom display followed by attractive fruit in autumn and winter, which provides food for birds. Wild crabapple (Malus sylvestris) is a native UK tree of hedgerows and woodland edges; ornamental varieties like 'John Downie', 'Golden Hornet', and 'Red Sentinel' are widely grown for their fruit. The rosy apple aphid is the most dramatic cause of leaf curl on crabapple in spring, producing tightly curled, pink-tinged leaves that persist through summer.

Rosy apple aphid

The rosy apple aphid (Dysaphis plantaginea) is the most damaging aphid on crabapple; colonies of small, grey-pink aphids build up on the undersides of the young leaves from bud burst in April and cause the leaves to curl tightly downward and inward, often turning purplish-pink. The distorted leaves are persistent: even after the aphids leave the tree in June and July to migrate to their summer host (plantain, Plantago species), the curled, disfigured leaves remain through the summer. On fruiting varieties, rosy apple aphid also causes the fruitlets to remain small and distorted; severe infestations significantly reduce fruit quality. Control must be applied before the leaves curl tightly, because once curled the leaves protect the aphid colonies from insecticide sprays.

What to do

Inspect the undersides of leaves from bud burst; apply insecticidal soap, neem oil, or pyrethrin spray at the first sign of colonies, before the leaves curl. Apply a winter oil wash to the dormant bark in December to January to smother overwintering eggs. Remove nearby plantains (Plantago) to reduce summer hosts and reduce the following year's autumn egg-laying. Encourage natural predators with nectar-rich companion planting.

Powdery mildew

Apple powdery mildew (Podosphaera leucotricha) overwinters in the buds of crabapple and produces distinctive "mildewed shoot" symptoms when the buds open in spring: the young shoot tips emerge with a silvery-white powdery coating and the leaves fail to expand fully, remaining curled and stunted in a characteristic rosette at the shoot apex. These mildewed shoots are sometimes called "extension shoots" when affected early in the season. In summer, powdery mildew spreads to newly developing leaves, producing the classic white coating. Susceptible varieties are much more severely affected than resistant ones; some ornamental Malus cultivars have good mildew resistance.

What to do

Prune out and destroy mildewed shoot tips in spring; this removes the primary source of overwintering inoculum in the buds. Apply a potassery bicarbonate or sulphur-based fungicide at bud burst and again at 10-day intervals through spring and early summer on susceptible varieties. Choose mildew-resistant varieties for new plantings (Malus 'Evereste', M. floribunda, and M. x robusta 'Red Sentinel' have good resistance). Avoid high-nitrogen fertilising that promotes soft, susceptible growth.

Apple scab

Apple scab (Venturia inaequalis) causes dark, velvety, scabby spots on the leaves, often with a yellow halo; severely infected leaves distort, curl, and drop prematurely. Scab also causes dark, corky, cracked patches on the fruit skin. The disease is most severe in wet, cool spring weather when the fungal spores are spread by rain from overwintered leaves on the ground. Some crabapple varieties are highly susceptible to scab; others have good resistance. In the UK, apple scab on crabapple tends to be less damaging than on dessert apple varieties because crabapple is often grown for ornamental value rather than fruit quality.

What to do

Rake up and dispose of fallen leaves in autumn; the fallen leaves are the primary source of next year's infection. Apply a fungicide approved for apple scab (myclobutanil, tebuconazole, or sulphur-based products) from green cluster stage through to 6 weeks after petal fall, at 10-day intervals in wet weather. Choose scab-resistant varieties for new plantings. Improve air circulation through the crown by removing crossing branches.

Apple capsid bug

Apple capsid bug (Plesiocoris rugicollis) causes characteristic small, ragged holes and rusty-brown scars on the young leaves of crabapple in spring; as the damaged leaf tissue expands, the holes enlarge and the leaf distorts, producing a tattered, curled appearance. Capsid feeding also causes sunken, rusty corky patches on the developing fruitlets. Apple capsid bugs are pale green, 6 to 7 mm long, and very mobile; they overwinter as eggs in the bark and hatch in spring to coincide with bud burst.

What to do

Apply an insecticide approved for capsid bug control (pyrethrin or acetamiprid) at the green cluster stage in spring, before the bugs begin feeding on the young leaves. Encourage natural predators; ground beetles eat capsid bug eggs. On ornamental crabapples where fruit damage is not a concern, capsid feeding rarely causes serious aesthetic harm and treatment is often not necessary.

Frequently asked questions

Why are my crabapple leaves curling?

Crabapple (Malus species) leaves curl most commonly because of rosy apple aphid (tightly curled, pink-tinged leaves with pink-brown aphids on undersides from April), powdery mildew (white powdery coating on stunted, curled shoot tips), apple capsid bug (ragged holes and distortion on young leaves), or apple scab (dark spots followed by leaf curl and premature drop in wet seasons). Rosy apple aphid is the most dramatic cause; treatment must be applied before the leaves curl around the colonies.

What are the best crabapples for UK gardens?

For fruit-making: 'John Downie' (large orange-red fruit, excellent for jelly), 'Golden Hornet' (abundant yellow fruit, persists through winter). For ornamental and wildlife value: 'Red Sentinel' (dark red fruit lasting to February, very disease-resistant), 'Evereste' (pink blossom, orange-red fruit, excellent disease resistance). For ornamental foliage: 'Laura' (purple-red leaves, pink flowers). 'Evereste' is arguably the best all-round choice for most UK gardens.

How do I make crabapple jelly?

Simmer whole crabapples with water until pulpy; strain through a jelly bag overnight. Add 450g sugar per 600ml juice; boil hard until setting point (104°C). Pour into sterilised jars. No added pectin needed; crabapples are naturally high in pectin. The resulting jelly is clear amber-pink to deep red depending on variety; excellent with game, pork, lamb, and cheese.

How do I control rosy apple aphid on crabapple?

Act before the leaves curl: inspect from bud burst and apply insecticidal soap or pyrethrin spray at the first sign of colonies. Once leaves have curled, sprays cannot reach the aphids inside. Apply a winter oil wash to dormant bark in December to January to smother overwintering eggs. Remove nearby plantains (the summer host plant). Encourage natural predators through nectar-rich companion planting.