Apple scab and pear scab

Venturia inaequalis and Venturia pyrina
Apple scab and pear scab are fungal diseases that produce dark, scabby marks to form on the fruit and the leaves of apples and pears respectively.

1. Black or dark scabby marks on the fruit
2. Cracked and distorted fruit
3. Cracked fruit may rot
4. Yellow, then olive-green spots and marks on leaves, which darken over time
5. Affected leaves drop prematurely
6. Blistering and cracking on young shoots and stems

Both fungal diseases cause black or dark scabby marks to appear on the skin of the fruit, and discolouration and marks on the leaves. The fruit is still edible, although it doesn’t look very appealing or appetising. Because the fruit can crack, other diseases can get into these cracks and cause the fruit to rot.

When they cause blistering and cracking of young shoots and stems, these can provide entry points for other diseases, such as apple canker.

Both diseases are most common during a wet spring, but can appear whenever conditions are correct for the disease to develop. Scab marks can appear on the leaves at any time in spring and summer.

Apple scab and pear scab are two separate diseases, caused by very similar fungi, which affect one or the other. Apple scab cannot infect pear trees and vice versa.
Apple scab can also affect ornamental crab apples, Cotoneaster, Pyracantha and Sorbus. Pear scab can also affect ornamental pears.

• Apples
• Crab apples
• Pears
• Ornamental pears
• Cotoneaster
• Pyracantha
• Sorbus

Apple scab is caused by the fungus Venturia inaequalis, which overwinters on fallen leaves and on infected shoots and stems.

In spring, airborne spores are released from the fallen leaves and infected shoots, which are splashed by rain or carried in the wind to infect the newly emerging leaves. Then, a second type of spore spreads infection to other leaves, fruit and stems throughout spring and summer. These spores are airborne or are spread by rain splash.

The closely related fungus, Venturia pyrina, causes the equivalent disease on pears.

Try to keep trees growing as strongly as possible to help them fend off disease attacks. However, when large outbreaks of apple or pear scab occur, this may not prevent it. Early identification of affected leaves, fruit and stems is essential.

Prune out any badly infected and blistered stems and shoots when you see them and dispose of them either by burning them or put them in the council’s green waste bin. Don’t compost them.

Carefully pick up all affected leaves and fruit, especially during autumn to try and reduce disease carry-over through the winter, and dispose of them.

This may have limited effect if several apple or pear trees are growing close by, since the spores can be carried long distances by winds.

Very old trees, especially those that are no longer in the best of health, are more prone to scab than younger, healthy ones. If old trees are regularly affected with scab disease, it may be better to remove them and replace with new trees.

Unfortunately, there are no fungicides available to home gardeners to control apple scab and pear scab on edible crops.

You can help protect new growth and prevent the disease – and to a slightly lesser extent, control existing diseases – on ornamental plants by spraying with a good garden fungicide, such as Bayer Garden Fungus Fighter or FungusClear Ultra. This is usually only practical on small trees and shrubs, as you need to spray the entire tree.

Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to possible danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.

There are numerous scab-resistant varieties of apple, including ‘Ashmead’s Kernal’, ‘Discovery’, ‘Egremont Russet’, ‘Lord Derby’ and ‘Reverend W Wilks’.

Scab-resistant pears include ‘Beurre Hardy’ and ‘Josephine de Malines’.

Bear in mind that over time such resistance can break down.

• Secateurs
• Leaf rakes