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.
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. 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 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.
Purple dot - confirmed reports
Grey dot - reports of declining oaks not due to AOD
Blue square - reports of locations with declining oaks but cause is currently unknown
The map indicates areas where symptomatic trees have been identified from photographic evidence.
Managing Acute Oak Decline - advice on how to recognise the disease, 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.
Tree owners should keep an eye on the trees' safety as the condition progresses and the trees decline, and fell or prune them if they or their branches threaten to fall and cause injury or damage.
We ask woodland managers and forestry professionals to keep an eye out for the signs of AOD and to report any sightings using our Tree Alert form