Posted by Lewis Gibbs
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Acute oak decline

Profuse stem bleeding

Acute oak decline (AOD) is a condition known to be affecting several thousand oak trees, mostly across East Anglia, the Midlands and South East England. It affects both of Great Britain’s native oak species: pedunculate oak (Quercus robur) and sessile oak (Quercus petraea); as well as other species of oak.

Records suggest that 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.


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

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

The Disease

Scientists from Forest Research, the scientific research agency of the Forestry Commission, 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 disease, how it spreads, and what other factors might be involved. This information will form the basis of appropriate management strategies.

We also have 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 determining 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.

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

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Ashdown Forest
East Sussex

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