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Quick facts

Common name: bronze birch borer

Scientific name: Agrilus anxius

What does it affect?: birches (Betulaceae)

Areas affected so far: not present in the UK

Origin: North America

 

What does bronze birch borer damage look like?

Symptoms include:

  • Discolouration and leaf thinning at the crown.
  • Dead leaves retained on the tree.
  • New growth from previously dormant buds, known as epicormic growth, on the main stems and larger branches.
  • Swelling and welts on the bark with rust-coloured sap produced when larvae bore through the wood.
  • D-shaped exit holes in the bark left by the adults emerging. This is an indication that the infestation is serious, as a lifecycle has been completed, and the tree is almost dead.

What is the bronze birch borer?

Adult birch borer beetles are also known as jewel beetles because of their metallic bronze colour and they’re between 7-12mm in length. They live for 23 days as adults and are strong fliers, this means they can spread quickly.

In its larval stage, the beetle creates galleries as it feeds on the wood which affects the tree’s ability to take on water and nutrients. The life cycle of the beetle depends on location but it has been estimated that in the UK it would take two years.

Where has the bronze birch borer impacted?

The bronze birch borer has not been found in the UK. In its native range of North America, the beetle is not a problem under normal conditions, but if it was to arrive in the UK European birch trees are much more susceptible as they have not evolved with the pest. European species planted in North America have already been affected by it.

What are we doing about it?

The bronze birch borer could be devastating to our native birches. That’s why birch trees can only be imported to the UK from countries free of bronze birch borer. It’s illegal to import live trees from the USA or Canada.

Birch wood imported from North America must be de-barked and have 2.5cm of sapwood removed.

To combat the spread of pests and diseases like the bronze birch borer we have:

  • Developed a UK Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK.
  • Lobbied the Government to improve biosecurity at border points to stop new pests and diseases entering the UK.
  • Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.
Horse chestnut tree discoloured to yellow after a leaf miner infestation

Trees woods and wildlife

What we are doing about tree pests and diseases

We are fighting back against pests and diseases. Find out what we're doing to prevent the spread and protect the UK’s trees. 

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What to do if you spot it

If you spot this post, please report it to the plant health authorities via TreeAlert if you are in Britain or TreeCheck if you are in Northern Ireland.