Why Do My Pear Leaves and Fruits Have Scab Marks?

Pear scab is one of the most common fungal diseases of pear trees, and it is particularly prevalent in wet springs and autumns. The characteristic dark, velvety blotches on leaves and rough, cracked scabby patches on fruit are caused by the fungus Venturia pirina — the pear equivalent of apple scab, though the two fungi only affect their own host species.

How pear scab infects the tree

The scab fungus overwinters in fallen infected leaves as fruiting bodies that release spores in spring, timed to coincide with leaf emergence and blossom. These primary spores are carried by rain splash and wind onto newly opening leaves and flowers. In wet conditions, new infections establish quickly — the spores need only a short wet period at the right temperature to germinate and penetrate young tissue. Secondary infections spread during summer through airborne spores produced on newly infected leaves, building up to affect the developing fruit.

Symptoms on leaves and fruit

On leaves, scab first appears as small, olive-green to brown velvety spots, often near the midrib. Heavily infected leaves yellow and fall early. On fruit, early infection at fruitlet stage produces rough, cracked scabby patches that can split the skin, making fruit vulnerable to brown rot. Infection late in the season causes small dark spots that are largely cosmetic. Fruit with surface scab is perfectly edible once the blemished skin is removed, but badly cracked fruit does not store well.

Autumn leaf collection

Removing fallen infected leaves in autumn dramatically reduces the primary inoculum available to infect the tree the following spring. Rake up leaves promptly as they fall and add them to a hot compost heap — hot enough to kill fungal spores — or bag them for collection. Do not leave them lying on the soil surface under the tree over winter. This single cultural measure has a significant effect on disease levels in subsequent seasons.

Improving air circulation

Scab thrives in the humid microclimate created by a dense, overcrowded canopy. Annual pruning that opens up the canopy and improves air flow through the branches reduces the period during which leaves remain wet after rain — the key window for spore germination. Avoid overhead irrigation which wets foliage unnecessarily. Where scab is severe every year, consider replacing the tree with a scab-resistant variety.