AFBI ask you to watch out for ‘Ash Sawfly’

Date published: 21 June 2022

Area of Expertise:

AFBI play a key role in protecting the health of trees and plants in NI. Threats from pests and disease are of particular concern at present for ash trees.

Adult ash sawfly

Ash trees are a very familiar part of our landscape. After hawthorn, they are the most common hedgerow tree in Ireland and are home to a wide variety of wildlife as well as a useful timber product, for example, for making hurley sticks. However, our ash trees are under threat from invasive pests and pathogens.

Ash sawfly caterpillars are voracious eaters and can strip leaves and trees bare
Ash sawfly caterpillars are voracious eaters and can strip leaves and trees bare
At this time of year, ash trees are subject to defoliation by hordes of small lime-green caterpillars. These caterpillars are the larval stage of ash sawfly (a relative of bees and wasps). They can build up in tremendous numbers and completely consume all the leaf material on a tree leaving behind a bare, skeletonised canopy.

Ash sawfly is a new species to Ireland. It was first recorded in Belvoir, Belfast in 2016 and has spread throughout the greater Belfast area and there are reports of it from as far afield as Co. Kildare.  Dr Archie Murchie, an entomologist from the Agri-Food & Biosciences Institute (AFBI), said: “It is amazing how fast the sawflies have spread. I cycle along the Lagan towpath and you can see caterpillars all along the path.”

At this time of year, ash sawfly caterpillars migrate down the trunk from the branches to pupate in the soil or to attack a new tree
At this time of year, ash sawfly caterpillars migrate down the trunk from the branches to pupate in the soil or to attack a new tree
Ash sawfly can cause sporadic damage to trees on the continent and occasionally urban trees in Great Britain but in Belfast the trees are being defoliated year on year. Dr Murchie said:  “We are seeing consistent defoliation in Belfast ash trees and although the leaves will grow back, the trees’ growth is likely to be stunted. It may be that the sawflies have left their natural enemies behind, so there is nothing to eat them and regulate their populations.”

Another factor may be the interaction with another serious problem for ash, ash dieback disease. This fungal pathogen has swept through Europe and was first found in Northern Ireland in 2012. It can seriously damage and kill ash trees.

Ash sawflies can completely strip a tree bare of leaves. The leaves will grow back but consistent defoliation each year may stunt the tree’s growth.
Ash sawflies can completely strip a tree bare of leaves. The leaves will grow back but consistent defoliation each year may stunt the tree’s growth.
Dr Murchie said: “It is depressing to see the state of our ash trees with dead branches caused by ash dieback and defoliation with ash sawfly. If another invasive beetle pest called ‘emerald ash borer’ makes it to NI, we could lose the ash trees completely, in the way that elm trees were wiped out by Dutch elm disease.”

AFBI and the Department of Agriculture, Environment and Rural affairs (DAERA) are monitoring the spread of ash sawfly. Any sightings of ash sawfly can be logged on the TreeCheck web app, www.treecheck.net, which is run jointly by DAERA and the Department of Agriculture, Food and the Marine (DAFM) in ROI.

Notes to editors: 

AFBI is an arms-length body of DAERA delivering research and development, diagnostic and analytical testing, emergency response capability and expert scientific advice for DAERA and other government departments, public bodies and commercial companies in Northern Ireland, and further afield.

AFBI’s Vision is “Advancing the Local and Global Agri-Food Sectors Through Scientific Excellence”.

AFBI’s core areas:

  • Leading improvements in the agri-food industry;
  • Protecting animal, plant and human health;
  • Enhancing the natural and marine environment.

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