Sweet chestnut blight

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Imports of sweet chestnut trees from areas affected by sweet chestnut blight are banned (Photo: A Perez/WTML)

Chestnut blight has now been confirmed in areas of England on sweet chestnut trees. It was first discovered in in 2011, then again in early 2017 at nine sites in Devon and Dorset and in July 2017 in south east London.

Chestnut blight (Cryphonectria parasitica) is a fungus that infects and kills chestnut trees (Castanea species). It was responsible for killing most of North America’s chestnut trees (Castanea dentata) in the 19th and 20th centuries when it was accidentally introduced from Asia. It has also now become widespread across the European mainland since its introduction in the 1930s. In Europe it mostly attacks sweet chestnut (Castanea sativa).

What is sweet chestnut blight?

Symptoms

  • Stem girdling, where the canker surrounds the stem and kills branches, causing them to wilt.
  • Orange spores in bark cracks; orange tendrils can form.

Causes

  • The fungus Cryphonectria parasitica

Outlook

  • Killed an estimated 3.5 billion trees in the USA in the first half of the 20th century.
  • Tree losses less devastating across Europe so far but still significant.
  • The disease seems to be particularly slow moving in the UK. Some of the recently identified infected trees had been imported and planted over 20 years ago and the infection seems to have stayed within that planted population of trees rather that spreading out rapidly.
  • There is a phenomena associated with this disease called ‘hypovirulance’. This results 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 preventing it from producing spores. This allows the trees to recover from infection.

Import and movement restrictions

The government introduced tighter controls for all imports of sweet chestnut (Castanea sativa) in November 2013 in response to the increased threat from sweet chestnut blight. Over the past few years this harmful fungal disease has decimated commercial crops in some European countries and has the potential to seriously affect sweet chestnut in our woodlands.

As a result anyone now moving sweet chestnut trees into, out of, or within, England and Scotland must ensure they hold the necessary plant passport confirming the plants have been grown in an area or country officially shown to free from the disease. In addition, the latest findings in England have resulted in movement restrictions of sweet chestnut material including plants, logs, branches, foliage and firewood out of, or within, six zones in Devon and Dorset. Full details of the specific zones can be found on the Forestry Commission website.

Report it

If you think you’ve spotted this disease please inform the Forestry Commission using the Tree Alert reporting tool. Three good-quality digital photographs are required to aid identification.

For more information visit the Forestry Commission.

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