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What is apple scab?

apples with apple scab
Unsightly apple scab may look like it only attacks the fruit, but it can damage the tree
Image: Shutterstock/ Evg Zhul

Apple scab is a common fungal infection which affects apple and pear trees. It attacks both leaves and fruit, and though it doesn't immediately threaten the tree, an uncontrolled infection may weaken it, making it more susceptible to other diseases.

Fungus

apple scab affecting leaves
The windborn culprit of apple scab causes blotches and eventually lowers resistance to disease
Image: Shuttertock/ Tatahnka

The culprit 'Venturia Inaequalis' is a windborn fungus that overwinters on fallen leaves and fruit. It also affects wild growing hawthorne as well as crab apple, mountain ash, and shrubs like pyracantha and cotoneaster, making it hard to protect your trees against infection from other plants in the local area.

The fungus which can also be transmitted by contaminated water, causes yellow blotches on leaves which, as spring turns to summer, darken through olive green, to dark brown. By July or August, the tree will shed affected leaves, reducing the plant's overall ability to photosynthesise, lowering its resistance to disease.

Fruits grow greyish raised or pitted scabs which, because they don't grow at the same rate as the fruit, cause your apples or pears to become misshapen as they grow, and can cause cracking and splitting.

Venturia is a major problem for commercial growers, who can lose up to 70% of their crop if the spring is particularly cool and damp. But as long as you're happy to cut the affected sections from your fruit, it shouldn't affect your apples' texture or flavour.

How do you prevent apple scab?

bardsey island scab resistant apples
Plant scab resistant varieties; you may be able to limit the chance of infection. 'Bardsey Island' apple is known to be scab and canker resistant
Image: Apple 'Bardsey Island' by Thompson & Morgan

If you're planting new trees and are worried about the possibility of apple scab infection, there's a wide variety of resistant strains from which to choose. Otherwise, unfortunately, your treatment options are limited.

Making sure you remove and dispose of fallen leaves and fruit can help to lower the severity of the infection because it reduces the number of spores that will settle on next year's new leaves. But if gardeners in neighbouring properties don't do the same, you could find yourself fighting a losing battle.

It's no longer possible to buy fungicides for trees whose fruit is intended for human consumption. You may wish to treat the tree, at your own risk, with a fungicide intended for ornamental trees, however you'll need to treat the entire tree, and even then, reinfection from affected trees in the area is a strong possibility.

Check out Thompson & Morgan's amazing array of apple trees, including mini and dwarf apple trees perfect for the patio. 100% satisfaction guaranteed or we give you your money back.