Skip to main content
Quick facts

Common name: emerald ash borer

Scientific name: Agrilus planipennis

What does it affect?: ash trees

Areas affected so far: not yet present in the UK

Origin: unknown

What does emerald ash borer damage look like?

Symptoms include:

  • Branches and leaves dying from the crown (top) down.
  • Horizontal fissures on the bark between 5 to 10cm in length which are made when the tree grows extra bark in response to the boring larvae.
  • New growth from dormant buds, usually extra foliage sprouting from the trunk, known as epicormic growth.
  • Damage from woodpeckers can increase as they strip away patches of bark to feed on the larvae.
  • D-shaped holes in the bark, about 3mm wide, made as the adult beetles emerge from the bark.

What are emerald ash borers?

Emerald ash borers are long, slender, metallic green beetles which grow between 7.5mm and 13.5mm long.

What happens to the tree?

The adult females produce between 60 and 90 eggs which they lay singly or in small clusters into bark crevices. They hatch in seven to 10 days.

When the eggs hatch the larvae burrow into the bark and begin feeding on the tissues that transport water and nutrients through the tree just under the bark. As they feed, they grow larger, between 26 and 32mm long, causing extensive damage to the tree.

The larvae feed voraciously until temperatures begin to fall in the autumn. When winter comes, they overwinter in tree bark or outer wood. They emerge as adults from May and start the cycle again.

Eventually, successive generations of larvae kill the tree as the water and nutrient transport systems become blocked.

Where has emerald ash borer impacted?

Emerald ash borer is native to eastern Asia and has been spreading westwards at a rate of 40km per year. So far it has been confirmed west of Moscow. It has also had an impact on huge areas of the US and Canada.

Typical ‘S’ shaped gallery 4th instar Emerald ash borer larva

Credit: David Cappaert / Michigan State University

How did emerald ash borer get here and what impact will it have?

The emerald ash borer is yet to reach the UK, but the biggest risk of introduction comes from imported wood, particularly firewood. This was the case in the US where campers often carry firewood from one area to another, speeding up the spread of the pest.

If the pest were to arrive in the UK, it would have a devastating ecological impact. Our ash trees are already under threat from ash dieback, so the introduction of the emerald ash borer could even make ash trees locally extinct in some areas.

What are we doing about it?

To combat pests and diseases like the emerald ash 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. 

Learn more

What to do if you spot it

If you spot the signs and symptoms of this pest, report it to the plant health authorities via TreeAlert if you are in Britain and TreeCheck if you are in Northern Ireland.

More pests and diseases: