Sweet chestnut blight (Cryphonectria parasitica)

What does sweet chestnut blight damage look like?

Sweet chestnut blight enters the tree through wounds and fissures. In cases where the tree has been grafted it occurs around the grafting point.

Symptoms include:

• Cracks in the bark that develop into dark, sunken cankers.
• Stem girdling, where the canker surrounds the stem and kills branches, causing them to wilt.
• Brown wilted leaves that remain on the tree above the canker.
• Orange fruiting bodies on the bark. These can produce long orange growths known as tendrils in humid conditions. These tendrils produce the spores which spread the blight.
• The cankered bark can become bright brown on younger branches in contrast to the usual greenish colour.

What is sweet chestnut blight?

Sweet chestnut blight is a fungus that attacks the bark of chestnut trees.

Where has sweet chestnut blight impacted?

Sweet chestnut blight devastated chestnut forests in the eastern US during the first half of the 20th century. It is estimated that it killed 3.5 billion trees after being imported from Asia.

It was accidentally imported to Italy in the 1930s and has been spreading in Europe since.

What impact will sweet chestnut blight have?

Sweet chestnut blight can kill a tree within a few years, but it seems to be slow moving here in the UK. Infections seem to stay within planted populations of infected trees rather than spreading out rapidly. That said, the introduction of more infected trees from abroad could speed up any spread.

A positive is that there is a natural phenomenon associated with sweet chestnut blight called ‘hypovirulence’. This is when the fungus is infected by a naturally occurring virus which makes it less aggressive by limiting the growth of the pathogen in the bark and prevents it from producing spores. This allows the trees to recover from infection.

What are we doing about it?

To combat the spread and introduction of pests and diseases like sweet chestnut blight we have:

• Developed a UK and Ireland Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK.
• Lobbied the Government to improve biosecurity at border points to stop new pests and diseases entering the UK.
• Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.