Q What is scab?
A Apple scab and pear scab are diseases that affect both leaves and fruit.
Caption: Unlike bitter pit, scab is only seen on the skin not the fruit
Q How do I recognise scab?
A Leaves develop dark greenish-brown spots or patches and may fall prematurely. Dark or corky patches can appear on fruit. If extensive, the corky patches crack, often in a pattern of small squares, causing considerable damage to the fruit. On badly affected trees the twigs will develop blistered swellings that burst in spring, releasing disease spores.
Q What causes scab?
A The fungus, Venturia inaequalis, affects apples, and the related V. pirina affects pears. The disease is likely to be worse in mild, damp weather and some varieties are more susceptible.
Q How serious are apple scab and pear scab?
A A mild attack will cause only cosmetic damage, but a severe attack will weaken the tree and spoil a lot of the fruit. Damage to shoots by scab can also provide entry points for the spores of canker, a more serious disease.
Q Will it spread to other types of garden plants?
A Apple scab and pear scab only affect these trees, but related fungi, such as pyracantha scab, will attack other plants.
Q Can the damaged fruit be used?
A Yes. Peel off the scabby bits. The affected fruit can usually be stored successfully unless it is badly cracked.
Q What about resistant varieties?
A Any variety can get scab, but good varieties showing more than average resistance include the following. Apple: 'Discovery', 'Egremont Russet', 'Falstaff', 'Pinova' and 'Red Devil'. Pear: 'Beurré Hardy' and 'Conference'.
Q Are there any varieties to avoid?
A The following varieties are particularly susceptible to scab. Apple: 'Bramley's Seedling', 'Cox's Orange Pippin', 'Gala', 'James Grieve' and 'Laxton's Superb'. Pear: 'Williams' Bon Chrétien.
Q What about crab apples?
A Scab can also attack crab apples, and 'John Downie' is very susceptible.
Q How can I control the disease?
A Once established, it cannot be controlled that season.
Q What can I do to prevent it?
A Clearing up and burning fallen leaves from infected trees reduces the numbers of spores available to reinfect trees next season. With badly affected trees, cutting out twigs with scabby swellings will also help.