Apple scab: how to recognise and treat it

Disease

Apple scab — Photo: Shuhrataxmedov, CC BY-SA 3.0, Wikimedia Commons

Symptoms

Olive-green, velvety spots or blotches on the leaves in spring and summer.
Brown to black scabby patches on the fruit, which may crack as the fruit grows.
Blistered and cracked bark on young twigs.
On pears a related fungus causes the same signs; the apple and pear fungi do not infect each other's host.

Organic treatment

Rake up and destroy or compost fallen leaves, where the fungus overwinters.
Prune out blistered twigs and remove infected fruit.
Copper- or sulfur-based protectant sprays before infection; they do not cure spots already present and sulfur can scorch some cultivars.

Chemical treatment

Fungicide with captan applied from spring onward; follow the label dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

Grow scab-resistant cultivars such as 'Liberty', 'Enterprise', 'Topaz' or 'Discovery'.
Shred fallen leaves with a mower before bud break in spring.
Avoid overhead watering so leaves dry quickly.

Plants it affects

Sources

Figures checked against these sources.