Acute oak decline (AOD) is a condition known to be affecting several thousand oak trees, mostly across East Anglia, the Midlands and Southern England as far west as Somerset. 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.
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 condition, how it spreads, and what other factors might be involved. This information will form the basis of appropriate management strategies.
We have also recorded a highly significant co-occurrence of the native buprestid or oak jewel beetle (Agrilus biguttatus) with the lesions in symptomatic trees. Research 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 our Forest Research agency. It will increase scientific understanding of the condition, 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.
The map indicates areas where symptomatic trees have been identified from photographic evidence.
General advice is to leave infected trees in place and continue to monitor them unless there is immediate concern about safety. 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 appear to be infected on a site, and most are of the same oak species, it may be prudent to fell and destroy the infected individuals – to keep infection levels low and reduce the risk of infecting healthy trees.
Managing Acute Oak Decline - includes more detailed advice on how to recognise the condition, what to do about it, and how to minimise the risk of spreading it.
We encourage people who work in or visit areas with affected oak trees to help us limit the spread of the condition by not touching affected trees if possible, cleaning their footwear between woodland visits, disinfecting tools after working on trees in affected areas, and not taking any plant material such as leaves and sticks out of affected woodlands.
We ask woodland managers and forestry professionals to keep an eye out for the signs of AOD and to report any sightings.