Ash sawflies eating way through Meath

Trees being stripped of foliage in parts of county


A Kiltale man is highlighting the damage that ash sawflies have done to ash trees in his area and has warned of potentially serious further damage they could do to ash trees in county Meath.

Cormac Reilly, who headed up Bayer CropScience in Ireland, saw adult ash sawflies, which are related to bees, lay eggs in trees in May. The eggs hatch into caterpillars which then proceed to completely eat all of the remaining leaves on the tree. This leaves them more at risk to serious diseases such as ash dieback, which can seriously damage or even kill ash trees.

Cormac also went on to explain that while the flies themselves pose little threat to mature trees, they could have a negative impact on younger trees.

“Because they eat the leaves on younger trees, this could stunt their development. They’ve completely eaten the leaves on some of my trees and they haven’t grown back yet.”

Cormac O'Reilly in Kiltale.

There are woods in Meath where they have become so rampant that the caterpillars fall of the trees like rain. You actually need an umbrella to walk underneath them because there is so many of them, Cormac states. The problem is particularly prevalent around Kiltale and Dunsany at present.

The flies first arrived on the island of Ireland in 2016 when they appeared in Belfast.

Dr Archie Murchie, an entomologist from the Agri-Food & Biosciences Institute (AFBI) there, said: “It is amazing how fast the sawflies have spread.

He 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 Ireland in 2012. It can seriously damage and kill ash trees.

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 Northern Ireland, we could lose the ash trees completely, in the way that elm trees were wiped out by Dutch elm disease.”


Ash sawflies (Hymenoptera: Tenthredinidae)

Ash sawfly larvae are white or cream colored and grow to about 3/4 inch in length. Although sawfly larvae are caterpillar-like, they can be distinguished by the presence of seven pairs of prolegs on the abdominal segments and a bead-like head that seems to set apart from the body.

Life cycle ash sawflies

Ash sawflies spend the winter as pupae in the soil. Adults appear in very early spring and lay eggs in slits cut along the outer margin of young leaflets. Newly emerged ash sawfly larvae chew small holes in the leaflets. Older larvae consume the leaf material between the leaf veins creating damage that appears as skeletonization. Large numbers of larvae may cause considerable defoliation in a very short period of time. Ash sawflies have only one generation per year. Larvae that finish feeding in late May or early June drop to the ground and burrow a short distance into the soil to wait until the following spring.

Damage caused by ash sawflies

Infested trees usually recover from defoliation as lost foliage is replaced by new foliage on healthy, vigorous trees. Therefore, control is seldom warranted. Also, by the time obvious damage is observed, it is usually too late for effective control.

Management of ash sawflies

The best management for ash sawflies is to maintain tree health and vigor through watering, mulching and other recommended cultural practices.

When control is justified, such as on stressed or newly transplanted trees, insecticides can be used. Timely treatment while the larvae are still small, can prevent feeding damage symptoms. Begin checking ash tree foliage for larvae in early May.

Source: Iowa University