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Phytophthora - The Problem

Whilst initial occurrences did not appear to be serious, experiences of the disease in USA and recent developments in the UK mean that we should be concerned and take a very cautious approach.

In the USA ramorum disease has been shown to affect the bark of trees causing large cankers which, when they encircle the trunk, lead to the death of the tree. This symptom has led to its common name in USA of 'Sudden Oak Death'. This is not a helpful name as it is not always sudden, it affects a wide range of tree and shrub species as well as oak and doesn't always lead to death. However, it has caused widespread tree losses in USA where it has now reached epidemic proportions and is extremely difficult to control. Therefore in Britain and Europe it has been designated a notifiable disease and Defra and the Forestry Commission are taking measures to control the disease at an early stage.

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Ramorum disease has a very different biology to Elm Disease (which is spread by beetles) and is not spread in the same way. However, it has the potential to cause widespread losses to a wide range of species and our damp windy climate could provide an effective means of spread.

 

Petiole and leaf base necrosis on Rhododendron

 

 

  

Rhododendron leaf blight

 

 

 

Aeiral dieback on Rhododendron

 

 

 

(above photos courtesy of Defra / Central Science Laboratory)

Phytophthora kernoviae has been found on a number of sites in Cornwall, South Wales and the North West of England and has caused serious damage. On Rhododendron, affected shoots turn black, wilt and leaves drop off. On beech, black bleeding spots occur on the trunk of affected trees, sometimes reaching several metres up the trunk. Trees and shrubs can be killed quite quickly after initial infection. It has also been found on our native Bilberry both on open heathland and in woodlands.

In late 2009 Phytophthora ramorum was detected on larch plantations in east Cornwall and Devon where it appears to be causing serious damage to Japanese larch (Larix kaempferi). Infections in larch are now more widespread with plantations in Wales particularly badly affected.