Acute oak decline

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Acute oak disease (Photo: WTML)

Acute oak disease is a relatively new condition but is on the increase (Photo: WTML)

Acute oak decline is thought to have been affecting our native oak species for around 20-30 years.

What is acute oak decline?

Acute oak decline affects mature English and sessile oak trees (Quercus robur and Q.petraea) of at least 50 years old but has been spotted in younger trees with a diameter of 10-12cm.


  • Black weeping patches on stems and trunks
  • Longitudinal splits or fissures in the bark at the site of the bleeds
  • Lesions and necrotic tissue underlying the bleed points
  • Larvae can weave a path between the inner wood and outer bark
  • Canopy health seems fine in early stages but grows visibly thinner as trees decline


  • There are a number of theories as to the cause including abiotic factors such as drought stress, and biotic factors such as bacterial infections in association with a bark beetle. The individual trees may have a predisposition to decline from an earlier abiotic event, weakening the tree and enabling biotic agents to establish


  • It appears that many trees are capable of recovering from the disease but individuals that are severely affected die within 4-5 years of developing symptoms
  • Woodland Trust sites are included in a national field survey being conducted by Forest Research and Rothamstead Research to provide background data on the extent and spread of this disease
  • A new research project launched in March 2016 called ‘Purpose’ aims to find answers to the problem of AOD. It is led by the University of Reading and also includes researchers from the universities of Oxford and York, the Centre for Ecology and Hydrology, Forest Research, and the James Hutton Institute

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.

Trees face huge challenges

With more new pests and diseases reaching our shores tackling pests and diseases is now an urgent priority

Learn about the threats