Why do my apples have black scabby patches?
The fungal disease behind cracked, corky black patches on apples and olive blotches on the leaves, why wet springs make it bad, and the leaf clearance that breaks its cycle.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 3 min
Short answer
Apple scab. Olive-brown blotches on the leaves in spring, then black corky cracked patches on the fruit. It overwinters on fallen leaves, so the effective control is to rake up and remove every leaf in autumn, prune to open the crown so it dries faster, and grow scab-resistant varieties in a wet garden. The fruit is edible; cut out the scab.
Scab is the commonest apple disease in the UK because our springs suit it perfectly: spores are released from last year's fallen leaves during wet weather from bud break onwards, and infection needs the leaf to stay wet for a number of hours. That means the disease is bad in a wet spring and mild in a dry one, and it means everything you do is aimed at reducing the spore source and helping the tree dry out.
Step by step
- Confirm the symptoms.Olive-green to brown velvety blotches on leaves from spring, often with early leaf fall. On fruit, dark scabby patches that go corky and crack, sometimes distorting the apple. On twigs, small blisters that split.
- Distinguish it from bitter pit and from canker.Bitter pit is small sunken brown spots with brown flecks in the flesh underneath and no fungal blotching. Canker is a sunken cracked area on woody stems with a raised rim, not on the fruit surface.
- Rake up and remove every fallen leaf in autumn.This is the control that matters. Scab overwinters on leaf litter and releases spores in spring. Rake, bag and remove — or shred and hot-compost — rather than leaving leaves under the tree.
- Prune to open the crown.Air movement and light dry the leaves faster, which shortens the wet period infection needs. Removing crossing branches and thinning a dense centre reduces scab measurably.
- Remove scabbed shoots in winter.Twig lesions carry the disease over as well as leaves. Cut them out while pruning.
- Do not overfeed with nitrogen.Soft sappy growth is far more susceptible. Sulphate of potash is the fruit feed; heavy nitrogen makes scab and canker worse.
- Choose resistant varieties when replanting.In a wet western garden this is the real answer. Discovery, Sunset, Ellison's Orange, Lord Lambourne and modern bred-for-resistance varieties suffer far less than Cox and Gala, which are notably susceptible.
- Keep the fruit and use it.Scabbed apples are edible. Cut the affected skin away. They do not store well, because the cracks let rot in, so eat or cook them first.
- Treat spraying as marginal in a garden.Effective chemical control means repeated applications timed to wet periods from bud break onwards, which is not realistic for a garden tree. If you use anything, check that it is currently approved for edible apples and follow the label exactly.
Tips
- Scab is worst in wet springs and in still, enclosed, humid gardens. The same tree in an open windy site suffers far less.
- A mulch laid over the ground in late winter buries some of the remaining spore-bearing leaf litter and reduces infection a little.
- Pears get their own version — pear scab — which behaves identically and is managed the same way.
- Scab damage on the fruit surface does not usually reach the flesh; it is a keeping-quality and appearance problem, not a food safety one.
Common mistakes
- Leaving fallen leaves under the tree over winter — That litter is the source of next spring's infection. Removing it is the single most effective control available to a gardener.
- Feeding a scabby tree with a nitrogen-rich fertiliser — It produces soft growth that is much more easily infected, so the disease gets worse rather than better.
- Composting scabby leaves in a cool heap — A cool garden heap does not reliably kill the fungus, so the spores come back with the compost. Hot compost, bag or council green waste.
Questions people ask
Can I eat apples with scab?
Yes. Cut away the scabbed skin. The flesh underneath is normally fine, though badly cracked fruit lets in rot and should be used quickly rather than stored.
How do I get rid of apple scab permanently?
You cannot eradicate it from a garden, but autumn leaf clearance, an open pruned crown and a resistant variety reduce it to something that barely matters in most years.
Why is scab worse some years?
Infection needs prolonged leaf wetness in spring. A wet April and May produce a bad scab year; a dry one produces almost none.
Does scab kill the tree?
No. Severe repeated infection weakens a tree by causing early leaf fall and reduces cropping, but it is not fatal.