Apple scab and pear scab

Apple scab and pear scab are two fungal diseases that causes dark, scabby marks on the fruit and leaves of apples, pears and some other ornamental fruits. They are so similar that they are dealt with in the same way.

Apple scab

Quick facts

Common name Apple scab
Scientific name Venturia inaequalis, Venturia pirina
Main symptoms Dark, scabby marks on fruit and leaves
Plants affected Apples, pears, some other trees and shrubs 
Caused by Fungus
Timing Mid-spring onwards

What are apple scab and pear scab?

Apple scab is a disease caused by the fungus, Venturia inaequalis, that spreads by airborne spores and survives the winter on fallen leaves. Expect scab marks to appear on leaves from mid-spring until leaf fall in autumn.

This is a disease specific to apples and other trees and shrubs including Cotoneaster, Pyracantha and Sorbus.  A closely related fungus, Venturia pirina, causes a similar disease called pear scab on fruiting and ornamental pears only.

Symptoms

You may see the following symptoms:

  • On leaves: Patches of olive-green spots or blotches appear, which are initially velvety as they release airborne spores, and then darkening. Affected leaves often fall prematurely
  • On young shoots: Infections cause blistering and cracking that can then provide entry for the apple canker pathogen
  • On fruit: Black scabby blotches develop and, as the fruit matures, these restrict expansion of the skin, leading to distortion and cracking. Light attacks only damage the skin and eating quality is hardly affected (though the disease is commercially very serious, because growers cannot sell scabby fruit). However, if the fruits crack as a result of scab they become prone to fruit rots and will not store well

Control

Non-chemical control

Pruning out young stems which are blistered, and disposing of fallen leaves and infected fruit will reduce the amount of fungus available to start infections in the next season. Unfortunately, this is generally of little value unless the trees are isolated, because the spores can be blown for long distances.

Some apple cultivars are resistant to infection, including:

A-C

‘Adam’s Pearmain’, ‘Alfriston’, ‘Ashmead’s Kernal’, ‘Barnack Beauty’, ‘Beauty of Bath’, ‘Brownlees Russet’, ‘Charles Ross’, ‘Cheddar Cross’, ‘Claygate Pearmain’, ‘Cockle Pippin’, ‘Cornish Aromatic’, ‘Cornish Gilliflower’, ‘Court Pendu Plat’, ‘Crawley Beauty’

D-F

‘D’Arcy Spice’,  ‘Discovery’, ‘Duke of Devonshire’, ‘Edward the Seventh’, ‘Ellison’s Orange’, ‘Emneth Early’, ‘Encore’, Epicure’, ‘Exeter Cross’

G-L

‘Golden Reinette’,  ‘Grenadier’, ‘Ingrid Marie’, ‘John Standish’, ‘King of the Pippins’, ‘King Russet’, ‘Lane’s Prince Albert’, ‘Lord Derby’, ‘Lord Hindlip’

M-Q

‘Melba’, ‘Merton Russet’, ‘Millers Seedling’, ‘Monarch’, ‘Mother’, ‘Newton Wonder’, ‘Orleans Reinette’, ‘Park Farm Pippin’, ‘Pinova’, ‘Ponsford’

R-Z

‘Rajka’, ‘Red Devil’, ‘Reinette du Canada’, ‘Resi’, ‘Reverend W. Wilks’, ‘Rosemary Russet’, ‘Ross Nonpareil’, ‘Rubinola’, ‘Santana’ (but is very susceptible to canker), ‘Stirling Castle’, ‘Suntan’, ‘Tom Putt’, ‘Topaz’, ‘Wagener’, ‘Wealthy’, ‘Wheeler’s Russet’, ‘Winston’, ‘Woolbrook Russet’.

Resistant pears include:

‘Beurre Hardy’, ‘Docteur Jules Guyot’, ‘Fondante d' Automne’, ‘Gorham’, ‘Hessle’, ‘Jargonelle’, ‘Josephine de Malines’, ‘Nouveau Poiteau’, ‘Catillac’, ‘Black Worcester’, ‘Souvenir du Congrès’.

Chemical control

Fungicides containing myclobutanil (Bayer Garden Systhane Fungus Fighter) can give good control when used according to the schedule recommended by the manufacturers.

For the most effective control, you need to cover the whole tree. Unfortunately, most gardeners will not have sprayers capable of treating large, old trees.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Biology

The fungus spends the winter on fallen leaves and also infected shoots if these are not pruned out. In spring airborne spores are released from the infected leaves, which causes the initial infections on the newly developing foliage. As these develop, they release large quantities of a second type of spore, also airborne or spread by splash from raindrops, which spreads infection throughout the growing season.

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  • pippin avatar

    By pippin on 13/06/2014

    Apple Scab has affected my very old cooking apple tree. Having read the online advice it appears there is very little I can do to beat this problem. Does this mean the apple tree should be felled? I assume I would need to site a replacement tree elsewhere?

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  • Whitehorse Vale avatar

    By Whitehorse Vale on 14/06/2014

    Felling your tree seems a rather drastic solution, considering just how long it takes a tree to grow, and become productive. If you replaced it, the same problem can occur again as the fungal spores causing the problem are air borne, so it does not matter where your tree is in the garden. Don't lose heart, all is not lost - a little patience, a bit of work and your tree will survive. I have the same problem with my apple tree this year. The wet weather and mild winter has created perfect conditions for all plant fungal diseases to multiply and spread. I am going to spray with the fungicide - Bayer Garden Systhane Fungus Fighter, as suggested under chemical control. It is quite a job to spray the whole tree, but looking on the bright side, any spray that falls on my roses and other trees will rid them of their fungal diseases too! In the last 30 years since my tree was planted, it has suffered apple scab, codling moths, hairy aphids, brown rot to name but a few. I have always managed to solve the problems and find a solution with a bit of research and expert advice. I try to help my fruit trees avoid any possible 'health problems' by feeding correctly and watering regularly, to ensure there are no deficiencies. Then keeping the garden tidy and free of leaf litter means the fungal spores and less places to grow. For me, my apple tree's continued growth and productivity have been ample reward over the years for my efforts. Hope you find this a positive contribution to your questions.

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  • anonymous avatar

    By anonymous on 16/06/2014

    I have planted a crab apple " John Downie". It had a full flush of blooms but is now suffering with curling leaves and black spots on the leaves and just looks sad. What is the best treatment .? I now only have a small garden on a new build estate and am trying to encourage birds another wildlife back into the area.

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  • Mr L avatar

    By Mr L on 19/06/2014

    I have the same problem on a "John Downie" the tree is 3 years old. I noticed their wasn't as much blossom as previous years and now the tree looks pretty poorly. It's still fairly small so I think I'll try to spray using the fungicide mentioned above. I also have a small garden (in Glasgow) which is wildlife friendy so I'll need to look into the potential impact of the spray.

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