Investigating the cause of extensive stem bleeding on oaks

A 2008 study to determine possible causal agents

News from Forest Research: December 2008

Photo
Assessing an oak with stem bleeding in the Forest of Dean

In 2005 Charnwood Borough Council requested help from the Forest Research Disease Diagnostic Advisory Service (DDAS) after becoming concerned about extensive stem bleeding on oaks which they thought might be infected with Phytophthora ramorum (Pr), the Sudden Oak Death pathogen. Forest Research specialists were able to rule this out as the cause, but with the continued increase in the number of symptomatic trees and tree deaths, they described the condition as ‘acute oak decline’. A key symptom is extensive stem bleeding, which is visible on affected trees. The same disorder was also reported from Hoddesdon Park in Hertfordshire, sites in Suffolk, Surrey and the Forest of Dean. Trees progress from apparently healthy to dying or dead in just 3–5 years.

In 2008 a small study was initiated to determine possible causal agents. Branch, twig, root and soil samples were taken from the affected sites for analysis. None of the roots showed symptoms of bleeding, but bacteria were consistently obtained from bleeding stems, suggesting that they play a key role in this condition.

Similar bleeding stem symptoms on Mediterranean oak have recently been reported in Spain and bacteria are also thought to be the cause of these occurrences. Questions remain about how widespread the problem is in Britain.


For further information please contact Sandra Denman at sandra.denman@forestry.gsi.gov.uk

                

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This and other news stories can be found in the December 2008 issue of FR News, our online newsletter.

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