Chronic oak dieback

A complex disorder or syndrome in which several damaging agents interact and bring about a serious decline in tree condition.

This resource will help you to identify trees suffering from chronic oak dieback and decline.

Disease overview

Stagheaded and declined oak yellowish canopy Warwickshire 2008

British oaks have been affected by a condition now known as chronic oak dieback or decline for much of the past century.  Pedunculate or English oak (Quercus robur) tends to be the most commonly affected. 

This disorder is widespread, prolonged and complex. The causes of the condition often involve abiotic factors for example poor soils, recurrent drought, high winds, disturbed environments and air pollutants. Biotic agents that are involved in the causes of this disease include insects and fungi that are destructive to weakened trees.

Predisposition to the disease is considered a very important aspect. Current specific evidence of the factors involved and how they affect the tree to make it susceptible to biotic agents is insufficient. Current research is addressing this so that a better understanding can be obtained and lead to management of the disease.

Disease details

  • Most commonly affects English or pedunculate oak (Quercus robur)
  • Caused by the complex and combined interaction of damaging abiotic and biotic agents including high winds, recurrent drought and opportunistic attack from insects and diseases on weakened trees
  • Also known as oak decline and dieback-decline

Chronic oak dieback is different to acute oak decline (AOD), which causes dark, weeping patches on the tree stems. Trees with AOD deteriorate rapidly and may die within four or five years.

Incidence and distribution

Oak with epicormics and recovery growthBritish oaks have been affected by dieback for much of the past century, caused by a complex combination of abiotic and biotic agents.

The most serious recent episode of chronic dieback occurred in 1989–1994, when drought damage weakened trees which were then attacked by the two-spotted oak buprestid beetle, Agrilus biguttatus, frequently leading to tree death.

Reported cases of oak decline are widely distributed. Since 2002 there has been a significant increase in reported sites with rapid and severe decline: these are cases of acute oak decline. 


  • Early foliage deterioration
  • Progressive death of branches over several years
  • Extensive dieback and secondary diseases in weakened trees leads to death in some cases
  • Affected trees often have dead branches or dieback in the crown

You can report oak trees with symptoms of dieback or decline to our Tree Health Diagnostic and Advisory Service.


Dieback occurs in oak trees when a number of damaging agents or events combine to weaken branches or trees. They are then susceptible to opportunistic attack from insects and diseases, or dieback caused by physiological stress or physical damage. See the Manion disease spiral model.

Our research

Forest Research has studied the role of different agents in oak dieback.

We are currently using a multidisciplinary holistic approach to investigating the environmental factors that weaken trees or predispose trees making them more susceptible to Chronic Oak Decline.

In some cases of Chronic Oak Decline certain biotic agents can play a dominant role, for example Armillaria. We are studying the role of Armillaria in oak declines, and the interactions between the various biotic and abiotic agents involved in this disease.

The definition and concept of Chronic Oak Decline are still evolving and the relationship between Acute Oak Decline and Chronic Oak Decline needs resolution.

Related resources

More about different forms of oak decline and dieback

If you suspect a tree is affected by chronic oak dieback you can report it using the Forestry Commission’s Tree Alert .

We can also help you identify diseased trees and provide advice on prevention and management. Please contact our Tree Health and Disease Diagnostic Advisory Service .


Dr. Sandra Denman