Apple and pear scab

What you are looking at

Olive-green to sooty black blotches appear on the leaves from late spring. They look velvety rather than glossy and their edges fade out instead of stopping at a rim. The leaf yellows around them and drops early, so a badly affected tree can be half bare by August.

On the fruit the same fungus makes rough brown corky patches. As the apple swells the corky tissue cannot stretch and splits, leaving a crack through the skin. The flesh underneath is sound.

Pears get their own species of the fungus, doing the same thing, and it also raises blistered scabby patches on the young shoots, which apples show less often.

Why some trees get it every year

Spores overwinter in the fallen leaves. Through spring, rain triggers them to fire upwards into the opening buds and infect the new leaves, and once the fungus is established on those leaves it produces a second kind of spore that splashes around the tree all summer whenever the foliage is wet.

Two things follow. Leaf fall under the tree is next spring’s infection, so clearing it up in autumn is a treatment rather than tidiness. And wet warm springs give bad years while dry ones give clean fruit, whatever anyone applied.

Cultivar matters more than either. ‘Cox’s Orange Pippin’ scabs in a wet British summer and ‘Discovery’ next to it stays clean, on the same soil, in the same year, with the same treatment. Anybody planting a new tree has the whole problem in their hands at that moment.

The sprays have gone

Mancozeb, which was the standard amateur treatment for scab, had its approval withdrawn in 2021, and myclobutanil went the same way. Neither is available and neither should be sought out. Most of what still ranks online for this term recommends one of them.

That leaves the leaf raking, the pruning and the cultivar choice carrying the page, and between them they handle it. A tree with an open centre, standing where air moves, cleared of its own leaf fall each autumn, carries light scab in a bad year and none in a good one.

Scab is also worth putting in proportion. It disfigures fruit and thins the canopy, and it does not kill apple or pear trees. Trees have carried it in British orchards for as long as there have been British orchards.

What to do about it

Rake up and remove the fallen leaves every autumn, or mow them where the tree stands in grass.

Prune in winter to open the centre out so the foliage dries quickly.

Cut out scabby shoots, especially on pears.

Thin off the worst-marked fruitlets in June.

Pare the scabs off the fruit and eat it, using the marked ones first because they store badly.

When planting, choose a resistant cultivar and place it where air moves.

What it gets mistaken for

Brown rot turns the flesh brown and soft and grows concentric rings of buff pustules on the surface. Scab stays dry and superficial.

Pear rust puts bright orange spots on the top of the leaf, each with a shaggy horned outgrowth on the underside, and it needs a juniper nearby to complete its life cycle.

Apple powdery mildew coats shoots, leaves and blossom in a white felt and stunts the growth from the tip back.

Bitter pit shows as small sunken brown spots scattered through the flesh and under the skin, with no surface roughness and no fungus.

Russeting is a natural brown roughness on the skin of certain cultivars, covering the fruit evenly rather than appearing as discrete blotches, and it is a feature rather than a problem.