Scab, everything you need to know about it

A fungal disease that strikes terror in the heart of orchards, scab can be diagnosed when brown spots appear on the fruits.

Advice on keeping it from appearing and getting rid of it.

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Scab, rather common for pear and apple trees

Although it also infects medlars and plum trees, it is most famous for infecting pear trees and apple trees for which scab is known to provoke devastation. Fruits on infected trees start showing brown spots that make the fruit rot as they spread across the flesh.

Spores from a fungus that overwintered on dead leaves are responsible for this contamination. First, the tree’s leaves are covered with velvety spots during the primary infection.

Things can stop there, but if it is a rainy summer, spores propagated by the spots on the leaves will germinate on the flowers and fruits of the tree. This is called secondary infection.

Best practices to fight scab

scabIn case of contamination, it will be difficult for you to save the current harvest, but a few good practices will help you eliminate any risk of a new infection in the following spring.

  • In fall, collect and compost fallen leaves.
  • Upon budbreak, treat your trees with Bordeaux mixture.
  • In case of frequent rain, treating with sulfur before and after the blooming will ensure that you have eradicated the spores.

Varieties that are generally invulnerable to scab

Scab is expected to appear in regions with rainy springs and summers. In those areas, best is to choose heirloom varieties that have learned how to resist scab: ‘Belle de Belle de Boskoop’, ‘Reinettes du Mans’ or ‘Reinette des Flandres’ for apples; and ‘Conference’ or ‘Williams’ for pears. Certain recent varieties such as ‘Ariane’ for apples have been developed to resist it.

Oppositely, varieties such as the ‘Golden’ or the ‘Orange Cox’ for the apples, and ‘BeurrĂ© Hardy’ or ‘BeurrĂ© Giffard’ for pears and their hybrids are particularly sensitive to scab.

Ask your local horticulturist when buying your fruit tree.

Laure Hamann