Scab

Venturia inaequalis and Venturia pyrina

also called Apple scab, Pear scab

Dark, corky patches on the fruit and leaves of apples and pears. Rake up fallen leaves in autumn and prune for an open, airy crown.

Fungus Serious Rain splashAirborne spores Spreads to neighbors

What you'll see

Olive-green to sooty-brown blotches on the leaves, with a woolly, indistinct edge rather than a sharp one.
Dark, rough, corky scabs on the fruit skin, which crack as the fruit swells.
Badly affected fruit is small, misshapen and splits, letting in brown rot and other rots.
Leaves yellow and fall early, thinning the crown by late summer.
On pears, blistered, cracked scabs also appear on young shoots and twigs, which apples rarely show.

Why it happens

A fungus that overwinters in fallen infected leaves — and, on pears, in twig lesions — and fires spores upward into the opening buds in spring. Wet leaves let those spores germinate, and each new lesion then produces summer spores that spread the attack through the season. It is quite distinct from potato scab, which is a soil bacterium affecting tubers, not a fungus of leaves and fruit.

Cool, wet springs are the making of it; the longer the leaves stay wet after bud burst, the heavier the infection. Crowded, unpruned crowns in a damp sheltered site keep the foliage wet for hours after rain.

Treating it

Rake up and remove every fallen leaf in autumn, or mow them and let worms take them in; this cuts next spring’s spore load dramatically.
Prune the crown open in winter so light and air reach the center and foliage dries quickly.
Cut out scabbed and cracked shoots on pears, which carry the fungus through winter.
Pick off and bin the worst affected fruit and leaves through summer.
Scabbed fruit is perfectly edible — cut the corky patch away and use it for cooking or juice.

Keeping it away

Plant resistant cultivars: Discovery, Sunset, Ellison’s Orange and the Pixie group among apples, Concorde and Beurré Hardy among pears.
Space and prune trees so air moves through, and avoid damp, sheltered hollows.
Avoid overhead irrigation and anything that keeps foliage wet.
Keep the ground beneath clear of leaf litter through the winter.
Feed moderately; soft sappy growth from too much nitrogen scabs more readily.

Who gets it

Apples and pears principally, with quinces, medlars, pyracantha and cotoneaster affected by their own closely related scabs.