Close up of the emerald ash borer

Emerald Ash Borer – Agrilus planipennis

Pests and Diseases

30th November 2020 | Info

Common Name: Emerald Ash Borer

Scientific Name: Agrilus planipennis

Type: Pest

Affects: Ash (Fraxinus spp.)

Current Impact: Not yet in the UK

Origin: Asia


The Emerald Ash Borer, also known as the EAB, is a long, slender beetle which may pose a significant threat to the Ash tree population in the UK. This is particularly problematic given the fact that the UK Ash population has not yet recovered from the devastating impact of the ever-present Ash Dieback threat.

Currently, the pest has caused a severe impact to Ash trees in Asia, the US and Canada, and recent updates suggest that in Europe, the beetle has reached Ukraine.

What are they? What do they do?

Emerald Ash Borers are metallic green beetles that can grow up to 1.35cm long, and it is their larvae that can cause damage or even death to Ash trees.

Adult female EABs can lay just under 100 eggs into the nooks and crannies of the bark of an Ash tree in one cycle, and these then hatch as larvae up to 7-10 days later.

Once they have hatched, the larvae bore their way into the bark of the tree and feed on its tissue that is essential for transporting its water and nutrients. During this time, they increase in size and can cause serious amounts of damage.

This process will often continue until temperatures begin to drop and the beetles then hide away throughout the colder months in the inner or outer bark of the tree. They eventually emerge the following spring/summer, and the cycle begins again.

More significant damage occurs after multiple generations of the larvae are present. Some trees may experience dieback or even death as their water transport systems get blocked to the point of no return.


Emerald Ash Borer on a leaf

What is the current spread?

Currently, the boring beetle has made its way across parts of Europe, with its most recent report being in Ukraine.

The spread of the beetle into continental Europe is concerning, since the UK is now more at risk of having the pest accidentally introduced.

According to and, the beetle can spread up to 25 miles per year. At the time of writing, that would mean the beetle would arrive in the UK in around 60 years time! However, all it takes is a single founder colony of beetles to make their way to the UK through accidental commercial/industrial transportation and the problem suddenly arrives on our shores. Once that happens, it may be very challenging to contain.

How can I tell if my tree has it? What are the symptoms?

As the pest has not yet made its way to the UK, we must remain vigilant and make ourselves aware of the symptoms. advise that if your tree is showing signs of this pest, then you must report it to TreeAlert (Great Britain) or TreeCheck (Northern Ireland) immediately.

Notable symptoms/signs of the disease are:

  • The dieback of (or dying) branches/foliage – In EAB infested trees, this often begins from the crown.
  • The thinning of foliage – you may notice your tree’s foliage thinning out and/or you may find that it turns yellow prematurely.
  • D-Shaped holes in bark – Emerging adult beetles may leave D-shaped holes.
  • Horizontal fissures forming on bark – These fissures can be up to 10cm wide and occur as the tree attempts to grow new bark in response to the damage being done by the beetle.
  • Epicormic growth – you may spot that there is extra foliage growing from the tree’s trunk or there may be new growth from what would have been dormant buds.
  • Woodpecker damage – Woodpeckers like to feed on the larvae so will strip away bark to get to them.


The bark of an ash tree that has been damaged by the emerald ash borer

What is being done to prevent it from reaching the UK?

Emerald Ash Borers could pose a severe threat to our already deeply impacted Ash tree population, which is one of the reasons why the introduction of the Emerald Ash Borer is being taken very seriously.

The greatest risk of the pest coming into the UK is through imported firewood, which is why Ash trees are now prohibited from being imported into the UK from any country outside of the EU, or any country that has recorded the presence of the pest.

Additionally, a recent development (in April 2020) has encouraged tighter control over national measures of the imports from EU countries, and for EU legislation to change. This should mean that the risk of importing infected wood should be lessened.

We must remain alert and report any cases if/when spotted.

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