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International Dendrology Society (IDS) Conference on Pests and Diseases

7 December 2012

Summary report of the meeting of the International Dendrology Society (IDS) Conference on Pests and Diseases:

Tree pests and diseases – crisis and responses

Temperate tree species are facing an increasing onslaught from pests and diseases. In the UK over the past ten years, the number of tree species, native and introduced, that are suffering from new pests and diseases has risen dramatically. To address this complex problem, the IDS organised a conference, held on 7 November 2012 at the Royal Botanic Gardens, Kew.

The problems

The remarkable increase of pests and diseases affecting trees in the UK is believed to result from two main factors. The first is global climate change, with more extreme weather conditions placing stress on tree species, making them more vulnerable to attack.  The second is the huge increase of global trade in plants for horticulture and the weak regulatory framework to control this from a plant health perspective.

The latest disease to hit the headlines in the UK is Ash Dieback caused by the fungus Chalara fraxinea a species that may have originated in East Asia. The first record of the disease in the UK was in March 2012 in a nursery on trees imported from the Netherlands. The next finding was in May and serious concerns emerged when symptoms were found in wild trees in October. In early November, the Forestry Commission undertook an intensive survey which found the disease at 115 sites within the UK with further sites suspected.

Other pests and diseases that have arrived in the UK over the past ten years or so include the bleeding canker and life miner affecting horse chestnut trees; chestnut blight, poplar rust; pear blister mite; conifer hedge decline caused by a combination of aphids, moths and mites; Dothistroma (red band) needle blight affecting Pinus sylvestris, and various species of Phytophora including P. austrocedrae which is attacking native juniper and P. alni affecting Alnus glutinosa.

The oak processionary moth, Thaumetapoea processionea is one of the new threats to native and introduced oaks – and a species that causes health problems for humans. The oak processionary moth is indigenous to southern Europe and has spread northwards throughout continental Europe.  The first recorded breeding population in the UK was located in west London in 2006. The introduction is thought to have been through nursery stock imported from the Netherlands, where it was first recorded in 1991.   Oaks are generally experiencing a range of diseases in the UK including ink disease caused by Phytophora cinnamomi, root rots, heart rot/decay, powdery mildew and secondary diseases such as twig cankers.

Finding solutions

In the UK, FERA is the executive agency of Defra with statutory responsibilities for delivering policy and inspectorate functions in relation to plant health. The Forestry Commission also has a statutory responsibility for inspection of wood imports to minimise the risk from foreign pests and diseases. Where outbreaks do occur Forestry Commission experts work with local authorities and landowners to contain and control any spread. The Commission licences tree felling across the UK to protect woodlands from further infection.

Monitoring the spread of each disease and decline is crucial. Botanic gardens can monitor the presence and behaviour of infecting organisms helping to gain a better understanding of the problems.  Sharing information on pests and diseases is extremely important both nationally and internationally. There is much to learn from experiences in other countries.

It should also be noted that botanic gardens curate between 30-40% of the world’s known plant species in their living collections, often not in the country or even continent in which they are native. This presents a significant opportunity to understand and predict when and where species may become pests, or when and where they may be susceptible to potentially introduced pests. A Sentinel Plant Network is a proposed structure under which individual gardens are able to act collectively to increase the predictive power of their collections.  Find out more about this here .


The global spread of invasive alien species is considered the second major cause of biodiversity loss. Tree pests and diseases are causing huge environmental and economic problems. Adding to the current  problems faced by trees in the UK, future pests that may cause problems include Pine Processionary Moth, Emerald Ash Borer, Asian and Citrus Long Horn Beetle, Bronze Birch Borer and new species of Phytophora.

Whilst international cooperation and control can be enhanced up through regulatory controls, it is vitally important for all organisations to work together to understand the threats to our trees and the wildlife dependent on them. The development of practical solutions will require integrated action.

A full report of the meeting will be published shortly on the IDS website

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