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Acute oak decline

Acute oak decline - profuse stem bleeding

Acute oak decline (AOD) is a condition  affecting several thousand oak trees, mostly across East Anglia, the Midlands and Southern England as far west as Somerset. It affects both of Britain's native oak species: pedunculate or 'English' oak (Quercus robur) and sessile oak (Quercus petraea) as well as other species of oak.

AOD was probably first observed in the UK in the 1980s, although literature studies indicate that a similar condition has been observed in continental Europe since 1918, spreading southwards and westwards since then.



Video: Identifying AOD symptoms - hosted by external party


AOD is characterised visually by dark fluid oozing from cracks in the bark, rapid decline of the tree, and the eventual death of affected trees. Death can occur within four or five years of symptoms first becoming visible.

Many affected trees also have characteristically D-shaped exit holes of the buprestid, or oak jewel beetle, in the bark. 

Typical symptoms

The Condition

Forest Research scientists have discovered previously unknown bacteria in affected oak trees, some of which they believe are playing a key role. They are continuing investigations to obtain a better understanding of the condition, how it spreads, and what other factors might be involved. This information will form the basis of appropriate management strategies.

They have also recorded a highly significant co-occurrence of the native buprestid or oak jewel beetle (Agrilus biguttatus) with the lesions in symptomatic trees. Adult Agrilus biguttatu (two spot oak buprestid). Alice Holt, Farnham, Surrey, EnglandResearch is looking at the relationship between the beetle and the bacteria, and whether the beetle is essential to the development of AOD, or merely coincidental. The beetle might be implicated in the spread of the bacteria.

The research

A research project by a consortium of research organisations is being funded by Defra. This £1.1 million project is led by Forest Research. It is increasing scientific understanding of the condition, its extent and distribution, and how it might best be tackled. The funding is being used to investigate, using DNA technology, the microbial assemblage associated with the lesions in the tree. The project is also investigating aspects of the beetle's behaviour, such as what attracts it to particular oak trees, and rearing the beetles in the laboratory so that we can understand more about their life cycle.

More-detailed information about the research effort, including annual newsletters published by the research team, is available on our Forest Research agency's website.

Outbreak stage

Map of confirmed locations of Acute Oak Decline up to March 2017

The map indicates sites where symptomatic trees have been identified from photographic evidence. Locations confirmed in 2016 are indicated by red dots, and brown dots indicate those confirmed from 2006, when records first began to be kept, to 2015.

More-detailed maps tracking each year's new confirmed cases are available from our Forest Research agency.

Treatment and management

Our advice is to leave infected trees in place and continue to monitor them, unless there is an immediate safety concern. If possible, cordon the trees off to prevent access. Try to minimise any contact with bleeds, to reduce the possibility of transferring the disease from tree to tree. If only a limited number of trees appears to be infected on a site, and most are of the same oak species, it might be prudent to fell and destroy the infected individuals to keep infection levels low and reduce the risk of infecting healthy trees.

Our Practice Note Managing Acute Oak Decline contains more-detailed advice about how to recognise the condition, what to do about it, and how to minimise the risk of spreading it.

If you work in or visit areas with affected oak trees, you can help us to limit the spread of the condition by:

  • not touching affected trees, if possible;
  • cleaning footwear between visits;
  • disinfecting tools after working on trees in affected areas; and
  • not taking any plant material, such as leaves and sticks, away from affected places.

Reporting suspected cases

Tree Alert iconWe ask woodland managers and forestry and tree-care professionals to keep an eye out for AOD and to report any suspected sightings with Tree Alert. Please note that Tree Alert requires you to upload one or more good-quality, well lit, close-up photographs of the symptoms.




Last updated: 19th December 2017