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Pests and Diseases

There are many pests and diseases which affect trees and shrubs in historic parks, gardens and landscapes. Some are very specific to a particular tree or shrub while others may use a whole range of host plants. In many cases these form part of a natural ecosystem. Problems can arise when pests or diseases are introduced because the trees or shrubs have no natural defence against these organisms and there are no natural predators. The pests and diseases can very quickly spread and reach proportions which are harmful, or even fatal, to the trees or shrubs.

This section covers:

In some cases these may be diseases which do occur naturally but which have mutated into a new and more aggressive form. In most cases invasive pests and diseases have been introduced from abroad and international trade makes this an increasing threat.

A good example of the speed with which invasive pests can spread is the case of the Horse Chestnut Leaf Miner (Cameraria ohridella). This micro-moth is believed to originate in Macedonia. It lays its eggs in the leaves of the Horse Chestnut (Aesculus hippocastanum.) and the larvae which hatch ‘mine’ the leaf, eating the leaf tissue between the upper and lower epidermis. When fully grown the larvae pupates within the leaf and a new moth emerges to lay more eggs. Several generations can hatch each year. Damage often first appears on the lowest leaves, moving successively up the tree until every leaf has been affected by the end of summer.

This insect was first discovered in Wimbledon in 2002 and rapidly spread throughout most of England and Wales by 2014. It is believed that the trees can cope with the level of damage it causes. Unfortunately it is hugely disfiguring and is very detrimental to the aesthetic appearance of a beautiful tree widely used in historic parks, public parks and cemeteries since its introduction around 1616.

Early in the summer the mines of Horse Chestnut Leaf Miner do not appear too bad but by the end of the year can totally destroy leaves
Early in the summer the mines of Horse Chestnut Leaf Miner do not appear too bad but by the end of the year can totally destroy leaves © Alan Cathersides

Monitoring and advice

Several bodies are involved in monitoring introduction of invasive pests and diseases and where possible controlling or containing them. They also provide advice on what to look out for and, where necessary, where to report sightings:

Current pest and disease concerns

For more detail about current pest and diseases in historic parks and gardens you can visit the Forestry Commission website, or click on the links below:

Future pest and disease concerns in historic parks and gardens

Pests and diseases which particularly need to be watched for are Sweet Chestnut Blight (Cryphonectria parasitica) and Asian Longhorn Beetle (Anoplophora glabripennis). There have been recent occurrences of these in the UK, but prompt action is believed to have eradicated the outbreaks.

Timber decay in historic buildings

The Practical Building Conservation book on Timber includes a chapter on the deterioration and damage of historic building timber by insects and fungi. It  covers:

  • Beetles, wasps, bees, and ants and other insects that may infest building timbers
  • Timber decay and types of wood rots
  • Photographs to help identify damage and causes

How you can help

Biosecurity for landscapes
© Forestry Commission
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