Over the past five years Forest Research, in collaboration with Rothamsted Research, has conducted a systematic survey to model the distribution of acute oak decline (AOD) in England and Wales. The results show that the condition currently affects several thousand oak trees, mostly across East Anglia, the Midlands and southern England.
The complex nature of the condition means it is often associated with other pathogens, as well as insect defoliators and the research has not yet concluded whether AOD kills trees or not. A large proportion of the infected trees monitored have entered remission suggesting some level of host resistance. We do not have information at the landscape level on the number of oak with AOD symptoms that die every year.
Since 2013, Defra has invested £1.1 million in research to understand the causes, distribution and scale of AOD in the UK. This includes work to investigate the bacterial species associated with the condition and to understand whether the Agrilus biguttatus beetle plays a role in the dispersal of these bacterial species. Early findings from this research are still inconclusive. There is currently no firm evidence of transmission by the beetle.
Earlier this year, Defra in collaboration with the Research Councils, Scottish Government and the Forestry Commission launched a further £2 million call for research proposals on ‘oak health’ and Phytophthora. The successful bids from this call are due to be announced shortly.