Pests and diseases

With a recent increase in findings of new pests and diseases, it is clear that Britain's trees are facing unprecedented threats. Our science indicates that climate change will create the conditions for even more pest and disease activity.

These heightened threats require us to take a more strategic approach to forest and tree health, and we recently formed a Biosecurity Programme Board with members drawn from a number of organisations with environmental interests in the private and voluntary sectors together with our own experts from the Forestry Commission and Forest Research.

Countryside poster

We and our partners working to control the threat from plant pests and diseases are also keen to encourage the public to help us prevent the transmission of diseases from one place to another when they visit the countryside. A poster has been produced to help the public understand what they can do to help, and anyone may download it to use in appropriate places, such as points of entry into public access areas.

The top pest and disease threats already present in Britain are: 

• Acute oak decline - a condition affecting oak trees in parts of England and Wales, in which bacteria, including one species previously unknown to science, are believed to be involved.
• Asian longhorn beetle - A wood-boring insect that can cause extensive damage to a range of urban and forest broadleaved trees.
• Bleeding canker of horse chestnut caused by the bacterium Pseudomonas syringae pathovar aesculi - a bacterium that kills many horse chestnut trees.
• Chestnut blight, a highly damaging disease caused by the fungus Cryphonectria parasitica, was confirmed in sweet chestnut trees in two nut orchards in Warwickshire and East Sussex in 2011.
• Dothistroma needle blight - Formerly known as red band needle blight, and caused by the Dothistroma septosporum fungus. Causes mortality and loss of timber yield in pine trees. Main host is Corsican pine, but lodgepole and Scots pine also increasingly affected. 
• Great spruce bark beetle (Dendroctonus micans) - is present throughout much of the Eurasian region, practically everywhere that spruce trees grow. It was first discovered in Britain in 1982.
• Horse chestnut leaf miner (Cameraria ohridella) - first found in Britain in 2002 in London, this moth's range has expanded to much of England and Wales.
• Oak pinhole borer (Platypus cylindrus) - once rare in Britain, populations grew in the south after the 1987 gales, when it took advantage of the glut of suitable breeding material.
• Oak processionary moth (Thaumetopoea processionea) - severely defoliates oak trees and can weaken them, making them susceptible to other pests and diseases. Outbreaks in west London and Berkshire.
• Phytophthora austrocedrae - Confirmed as the cause of dieback and deaths of juniper bushes in Northern England in 2011, this pathogen had previously been almost solely associated with Chilean cedar trees in South America. Juniper's conservation importance makes this a potentially serious development.
• Phytophthora kernoviae - so far confirmed only in Britain, Ireland and New Zealand, and only in a very few trees. However, the fact that it can infect beech and oak, as well as woodland under-storey species such as bilberry and rhododendron, makes it a forestry concern.
• Phytophthora lateralis - usually kills most Lawson cypress trees that it infects. First recorded in UK, in Scotland, in 2010, now present in Devon, Yorkshire, Northern Ireland and Republic of Ireland.
• Phytophthora ramorum - a fungus-like organism which attacks many trees and plants. The economically important larch is a host, and large numbers have had to be felled.
• Pine tree lappet moth (Dendrolimus pini) - has been discovered breeding in Inverness-shire pine plantation forests. It can be a serious defoliator of pines and other conifer trees in some parts of its native range in Europe and Russia.

Threats not yet present in the natural environment in Britain:

• Ash dieback - a fungal disease that causes crown death and wilting and dieback of branches.
• Citrus longhorn beetle - a wood-boring insect that can cause extensive damage to a range of urban and forest broadleaved trees. Very similar in appearance and effects to Asian longhorn beetle (above).
• Eight-toothed European spruce bark beetle (Ips typographus) - an insect that causes mortality, mostly in spruce trees.
• Emerald ash borer (Agrilus planipennis) - a wood-boring insect that causes widespread mortality of ash trees and loss of timber value.
• Pinewood nematode - a worm that can cause serious tree damage and mortality.

Detailed summaries of the status of these and other pest and disease threats are available from the following documents:

• Pests_established_in_UK.pdf
• Pests_newly_arrived_in_UK.pdf
• Pests_in_EU_posing_threat_to_UK.pdf
• Other_pest_threats_globally.pdf

Keep up with tree pest developments at www.twitter.com/treepestnews