Skip to main content

Scab Disease

Scab Disease, Scab

Holding Apple with scab

by Margalob. CC BY-SA 4.0

A close up of a hand holding an apple with apple scab
Various fungal species cause scab disease in plants. Each species tends to be specific to its host (the plant infected), however, all-cause similar symptoms in plants. Some of the most common Scab diseases are Apple and Pear Scab. The main symptoms involve dark lesions on the leaves, stems and fruits. The lesions of fruits crust over, forming a black scab, which ultimately turns sooty when the spores are produced. Scab diseases rarely kill plants, and the damage is mostly aesthetic. However, harmful infections can reduce the quality of crops, and overall growth may be stunted. Trees may weaken and be susceptible to infections by other pathogens.
Free download for your phone or tablet
Download on the App StoreGet it on Google Play


Dark irregular-shaped lesions which can be olive-green, purple or black. Lesions develop a sooty substance when spores are produced. Leaves turn yellow and fall from plants prematurely. Flower buds blacken and fall early. Fruits develop lesions which scab, dry, then crack open.

Growth factors

Spores are produced during wet weather, in most cases.


Greenish-brown blotches or blisters on leaves.
Premature leaf fall.
Blistered swellings on twigs
Dark spots or cracked and corky blisters on fruit.

Biological treatment

Removing fallen leaves from diseased plants can interrupt the disease cycle. Pruning out infected branches and burning them.

Chemical treatment

In foliage outbreaks, spraying with an approved fungicide once a fortnight from when the buds first break until the blossoms drop. If the wood is also infected, then the spraying will need to continue until harvest. Rigorous spraying can eliminate the apple scab by the third growing season. Be mindful when using fungicides, as they can be toxic. Always take care to read the label of the bottle.


The disease-causing fungi lie dormant during winter, either on plant debris or as small cankers and lesions on trees. When the spores are produced, they are carried to new hosts in the wind. Scab can also be spread during heavy rainfall. Both require prolonged wet surfaces to successfully infect a new host.


General hygiene around plants, e.g. cleaning gardening tools regularly and removing the dead material from the base of the tree. Try to take good care of the tree; Scab disease is often a sign of neglect. Regular pruning to encourage sufficient air circulation in the tree, allowing surfaces to dry quicker.

Affected plants


Malus spp.


Pyrus spp.

Poplar Tree

Populus spp.


Salix spp.


Pyracantha spp.


Olea spp.

Free download for your phone or tablet
Download on the App StoreGet it on Google Play

Plant Knowledge

Search our ever-growing knowledge base to find plants and information. Find out about pests and diseases you should be keeping an eye out for. Watch How to videos or follow step by step guides for tasks in the garden. Free download for your phone or tablet.
Download on the App StoreGet it on Google Play


About usCareersPrivacy policy

Candide is your guide to visiting UK public gardens. Find the best gardens, buy tickets and enter with just your phone. Download the app for offline tickets, community access and more.

Terms & ConditionsCode of Conduct

© 2022 Candide

Made in Bristol