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Ash Dieback (Chalara)


Susceptible species


How the disease is spread

First Finding

2012/2013 Survey

2014 Survey

2015 Survey

Current Findings

Distribution Map

Non Planting of Ash

Introduction of Reconstitution Scheme

Other eradication measures

North South Co-operation

All Ireland Chalara Control Strategy

All Ireland Chalara Conference

Information Meetings

Ongoing Information Actions


Research Group FRAXBACK

Spore Trapping

Breeding for Resistance

Modelling Ash Dieback

Ongoing Policy Review

Legislation - Initial national measures – 2012

Legislation - Update of national measures - 2015

EU Plant Health Law

Reporting Suspect Cases

TreeCheck App

Practical measures to avoid spread of Ash Dieback

Useful Websites



Chalara or Ash Dieback disease is a disease of ash trees caused by the fungus Hymenoscyphus fraxineus. The vegetative state of the fungus was previously referred to scientifically by the name Chalara fraxinea from whence the disease derived one of its common names - Chalara. (This disease should not be confused with ‘ash dieback’ syndrome, which is also present in Ireland)

Scientifically the disease is only relatively newly described.  Dieback symptoms in ash had been first noted in Poland in the early 1990s without any identifiable cause.  The disease was first described as a new species in 2006 and given a distinct name - Chalara fraxinea. The harmful sexual reproductive stage of the fungus producing the infective ascospores was however only discovered as recently as 2010.  It was first named Hymenoscyphus pseudoalbidus, a news species to science, but renamed Hymenoscyphus fraxineus in 2014. This is the pathogen responsible for the disease Ash Dieback.

In the intervening two decades the disease has spread rapidly across much of Europe, with the majority of European countries where ash is present now reporting, through the European Plant Protection Organization (EPPO), the presence of the disease.

The origins of the disease are as yet not certain but scientists have suggested the disease may have been introduced to Europe from eastern Asia.

Ash Dieback is not regulated in any Member State under the EU Plant Health Directive.


Susceptible species

To date the disease has only been found in ash. Our native common ash (Fraxinus excelsior) is susceptible to Ash Dieback disease, as are a number of other species of ash.

The disease can affect ash trees of any age and in any setting. The evidence also shows younger trees succumb far more rapidly whilst older trees can survive initial episodes of infection, possibly for many years.



Ash trees affected by the disease suffer wilting foliage, crown dieback and bark lesions.

The disease can kill an infected tree directly as over time necrotic lesions gradually encircle and permanently damage the phloem: (the innermost layer of bark) which is the layer of living tissue that carries organic nutrients to the others parts of the plant, or indirectly by weakening the tree to the point where it becomes more susceptible, and succumbs more readily to, attacks by other pests or pathogens, especially Armillaria fungi, or honey fungus.

There are a wide range of symptoms associated with Ash Dieback disease, the most visible include:

  • Necrotic lesions and cankers, often diamond shaped,  along the bark of branches or main stem;
  • Foliage wilt;
  • Foliage discolouration (brown / black discolouration at the base and midrib of leaves);
  • Dieback of shoots, twigs or main stem resulting in crown dieback;
  • Epicormic branching or excessive side shoots along the main stem; and
  • Brown / orange discolouration of bark.

Note: The symptoms described above are not exclusive to Hymenoscyphus fraxineus and may be attributable to a number of other causal agents or other factors, e.g. frost.

For more on symptoms see the Information Note on Chalara fraxinea Ash Dieback disease, below.


How the disease is spread

The fungus which causes the disease has a complex life cycle. Infection first makes its way into a tree when the spores of the fungus are carried in the air and land on healthy leaves over the summer months. The fungus then grows into the leaves and down into the leaf petiole or rachis, and progressively into twigs, branches, and the stem.

The infected leaves gradually wilt and blacken, but may remain on the tree for some time. These infected leaves then fall to the ground over the autumn and early winter months and the fungus produces a characteristic blackened ‘pseudosclerotial plate’ on the rachises. These blackened rachises harbour the disease overwinter.

In the sexual reproductive stage of the fungus, which takes place over the course of the summer and autumn months (June to October), very small mushroom-like fruiting bodies develop on the blackened rachises and decaying leaf litter from the previous autumn and winter. When mature, these tiny fruiting bodies release large quantities of microscopic spores into the air, some of which will land on the leaves of both healthy and previously infected ash trees to begin the cycle again.

Where the disease is already present in a locality further local spread is likely to be caused by spores borne on the wind, each year travelling many kilometres from the original source. There is also a risk of introducing the disease into a locality where it is not yet present (and where that locality is at a considerable distance from an existing source of infection) by bringing already diseased ash seeds or plants into that area for the first time.

Movement of larger diameter ash logs from infected areas is considered to be much lower risk so long as certain phytosanitary measures are properly implemented. These include ensuring the larger diameter logs being moved have no evident signs of the disease, e.g. lesions or staining, and that all leaves and foliage (whether living or dead) are completely removed on site before transportation.


First Finding

The first confirmed finding of the disease in Ireland was made on 12th October 2012 at a forestry plantation site in County Leitrim which had been planted in 2009 with trees imported from continental Europe. Shortly thereafter all the recently planted ash trees on that site were destroyed under Departmental supervision. The ash trees on another 10 sites where trees from the same batch were planted out (approximately 33,000 plants in total) were also destroyed as a precautionary measure.  


2012/2013 Survey

Following the first confirmed finding the Department initiated a specific programme of surveys of ash trees both in the locality of the infected plantation and nationwide. Results from a major survey over the winter months of 2012/2013 confirmed further positive findings. By February 2013 there were 46 confirmed findings of the disease made in young ash trees. These included confirmed findings in 26 forest plantations distributed over 11 counties, 14 in horticultural nurseries as well as 1 in a garden centre, 3 from roadside plantings, and 1 in a farm landscape planting.

Systematic surveys for the disease nationwide were undertaken by the Department over the course of 2013 in accordance with the International Standard ISPM No. 6, as were targeted surveys of hedgerows surrounding the first identified infected plantations. In October 2013 the first confirmed finding of the disease in a hedgerow in Ireland was made in a tree in a hedgerow at the original infected plantation in County Leitrim.  The Department, as a precautionary measure and with the consent of the affected landowners, then undertook additional works in the locality as part of its ongoing effort to prevent the establishment of the disease. These works entailed the felling and destruction of all hedgerow ash trees within 250 metres of the original infected forestry plantation.

Notwithstanding the positive effects at local level of the eradication actions undertaken to date, both by affected landowners supported by the Reconstitution Scheme or directly by the Department itself, the annual systematic surveys and targeted surveys as well as follow up inspections on suspected findings reported by concerned landowners or others, since 2013 has resulted year on year in a continuing rise in the number and geographic distribution of confirmed findings nationally.

By the end of December 2013 the total number of confirmed findings of the disease throughout the country had reached 113, including a second native hedgerow finding adjacent to a farm landscape planting (dating from 2004) in County Tipperary.


2014 Survey

In 2014 the continuing surveys increased the total number of findings to 143, including two additional native hedgerow findings, one in County Clare and the other in County Limerick.


2015 Survey

The Department repeated its systematic and targeted plant health surveys in relation to the disease over the summer months of 2015.  These included a targeted survey of forestry plantations with imported ash (97 locations) and a systematic survey of 376 National Forest Inventory points (153 forest locations and 223 hedgerow locations) across the country as well as surveys in horticultural nurseries, garden centres, private gardens, roadside / motorway landscaping plantings and farm landscaping / agri-environment scheme plantings.

The associated laboratory tests on material sampled during this survey was completed in October. The results indicated a further significant increase in confirmed findings in forest plantations, an increase in confirmed findings in native hedgerows and in roadside plantings, as well as an expansion in its known geographic distribution in 2015.


Current Findings

There are currently confirmed findings of the disease in 115 forest plantations distributed over 19 counties. In 2015 there were some 52 individual positive samples from trees in native hedgerows and some 76 individual positive samples from trees in roadside / motorway landscaping plantings. There are currently confirmed findings of the disease in native hedgerows in 12 counties and confirmed findings of the disease in roadside / motorway landscaping plantings in 13 counties.

Taken together this means that in terms of forestry plantations, private gardens, roadside / motorway landscaping plantings, and farm landscaping / agri-environment scheme plantings, the presence of the disease has been confirmed in 24 of the 26 counties in Ireland.


Number and location of confirmed findings of Ash Dieback disease in Ireland

(as of 25th January 2016)


No. by site type / county

Number of Confirmed


Oct 2012 to End of 2014

Number of additional Confirmed

Findings to date in



Total to date

(25 Jan 2016)


Forestry plantations




Horticultural nurseries




Garden centres




Private gardens




Farm  / agri- environment plantings





No. of counties with hedgerow findings




No. of counties with roadside / motorway findings





1 There are currently 115 plantations with positive samples distributed over 19 counties: Carlow, Cavan, Clare, Cork, Galway, Kildare, Kilkenny, Leitrim, Limerick, Longford, Mayo, Meath, Roscommon, Sligo, Tipperary, Waterford, Westmeath, Wexford, and Wicklow.

2 In 2015 there were 52 individual positive samples taken from trees in native hedgerows, with total confirmed findings currently distributed over 12 counties: Cavan, Clare, Donegal, Galway, Leitrim, Limerick, Longford, Monaghan, Roscommon, Sligo, Tipperary, and Wicklow.

3 In 2015 there were 76 individual positive samples taken from trees in roadside / motorway landscaping plantings, with total confirmed findings currently distributed over 13 counties: Clare, Cork, Dublin, Galway, Kilkenny, Limerick, Louth, Meath, Monaghan, Offaly, Tipperary, Waterford, and Westmeath.




Distribution map of confirmed findings of the Ash Dieback in Ireland

(as of25th January 2016). The locations of horticultural nurseries and garden centres are not depicted.

Added 29.01.16



Non planting of ash

In December 2012 the Department delisted ash as a tree species approved under the afforestation grant schemes and shortly thereafter delisted ash from the trees species approved under the agri-environment options scheme (AEOS, now GLAS). In 2013 the European Commission approved the Department's application to allow farmers participating in the current agri-environment schemes, who had concerns regarding ash plants planted under the schemes showing symptoms of ash dieback, to apply to remove the ash plants under force majeure. The National Roads Authority also agreed in 2013 to suspend the use of ash in any roadside/motorway plantings and since then it uses alternative species. Coillte also made a policy decision not to replant with ash.


Introduction of a Reconstitution Scheme

In March 2013 the Department introduced a Reconstitution Scheme (Chalara Ash Dieback) to restore forests planted under the afforestation scheme which had suffered from or which were associated with plants affected by disease. By the end of 2015 some €2.6 million had been paid out under the Scheme and over 715 hectares of infected and associated ash plantations had been cleared and replanted or was in the process of being replanting with alternative species. This has entailed the uprooting and deep burial of an estimated 2 million ash trees. These figures are expected to increase in the coming months as applications for the Scheme from more recently identified forestry plantations affected by the disease are processed by the Department.


Other eradication measures

In addition to the above eradication measures involving the removal and destruction of several thousand ash trees have been undertaken in roadside / motorway landscaping plantings, farm landscaping / agri-environment scheme plantings, and horticultural nurseries / garden centres.


North South Co-operation

As with plant health generally on the island of Ireland, an all-Ireland approach has been maintained under the North-South Ministerial Council (NMSC) between authorities in Ireland and Northern Ireland with ongoing close co-operation in all areas. This included the publication jointly by Minister of State Tom Hayes and the Northern Ireland Minister for Agriculture and Rural Development, Ms Michelle O'Neill, MLA, in July 2013 of an All-Ireland Chalara Control Strategy.


All-Ireland Chalara Control Strategy

The All-Ireland Chalara Control Strategy outlined four main objectives: 1) Reduce the risk of the disease becoming established in the wider environment, 2) Support research on modelling the spread of the disease and developing resistance, 3) Encourage engagement by industry, landowner, voluntary organisations and the general public, and 4) Building resilience in Woodland and in support of associated industries. The disease is regularly discussed at Ministerial level at the North-South Ministerial Council (NMSC). Day-to-day implementation of the strategy is co-ordinated by officials from the Department and the Department of Agriculture and Rural Development (DARD) in Northern Ireland through formal and ad hoc meetings of the NMSC Plant Health Sub-Group.


All Ireland Chalara Conference

In May 2014 an all-Ireland conference on the disease was jointly organised by this Department and DARD in conjunction with the Agri-Food and Biosciences Institute (AFBI), Northern Ireland and the Society of Irish Plant Pathologists. This conference was very well attended and brought together presentations and discussions on the latest scientific knowledge on the disease and input from stakeholders and other interested parties. The event underlined the commitment from both administrations to share the latest information available and to find long-term solutions which can deliver the best possible outcome.


Information Meetings

In May 2013 the Department, in conjunction with Teagasc, organised a total of 22 public information meetings. More than 800 people attended and information was provided on what to look out for and the implications in terms of clearance of a forest plantation. There was a large media pick-up on these events, including print, radio and television. Guidance on the symptoms of Chalara was placed on the Department's website and the GAA featured a full page awareness advertisement in their All-Ireland hurling final programmes in both 2013 and 2014.


Ongoing information actions

Advice continues to be provided by the Department’s Inspectors to foresters in the public and private sectors on the biology of the disease and recognition of symptoms as well as on the procedures around the clearance of affected forest plantations and infected nursery stock. Inspectors also regularly provide briefings for or attend information meetings for landowners and other relevant stakeholders and representative groups such as the IFA, the GAA, and the Ash Society.

Teagasc are planning to run 42 one-to-one forestry advisory clinics nationwide in January 2016. These annual clinics, which previously have had over 500 people attend, will again provide the Department with an opportunity to disseminate information on the disease and the strategy to control its spread



Research actions in Ireland

Scientific research on the disease both in Ireland and elsewhere in Europe, with a focus on developing ash tree breeding programmes to develop trees showing strong tolerance to the disease, is a key component in the strategy to combat the disease in the long-term.


Research group - FRAXBACK

The Department is a participant in the European Cooperation in Science and Technology (COST) funded action into the disease (FP1103 FRAXBACK COST is an intergovernmental framework for European Cooperation in Science and Technology, allowing the coordination of nationally-funded research on a European level.  FRAXBACK is a four-year COST action started May 2012. Many European countries have national research programs on Ash Dieback, focusing on numerous aspects of the biology and ecology of the disease. The aim of the FRAXBACK action is, through sharing and synthesis of available knowledge, to generate comprehensive understanding of Ash Dieback, and to elaborate state of the art practical guidelines for sustainable management of Fraxinus in Europe. Twenty-six European COST countries are participating in the FRAXBACK action including Ireland. Five non-COST institutions from China, New Zealand, Russia and Ukraine are also involved.


Spore trapping

As part of the 2015 Ash Dieback work programme the Department included a spore-trapping element aimed at detecting, quantifying, and establishing dispersal patterns around known positive locations. The study was conducted with the assistance of experts from the French National Institute for Agricultural Research (INRA) and based mainly in Tipperary and Leitrim where 192 spore traps were placed in the wider countryside for a week or two during the summer and removed and analysed for the presence of spores. Ash dieback spores were found in 14 spore traps.   


Breeding for Resistance

The Department is also actively supporting a number of other research projects into the control and management of the disease, in particular projects with a key long-term focus of developing an ash tree breeding programme to indentify trees that show strong tolerance and or resistance to the disease and the genetic basis for tolerance. In this regard, a five-year project was begun in 2013, the aim of which has been to indentify individual trees of ash which show resistance or tolerance to Ash Dieback and to use them for possible future breeding work and DNA screening by other institutes. The project, which is part funded by the Department, is being carried out by Forest Research, an agency of the Forestry Commission in the UK. The project involves 48 hectares of trial plantings over fourteen sites in the east of England and the mass screening of some 155,000 ash trees with fifteen different provenances from continental Europe, the UK and Ireland.  Over 14,000 Irish ash plants from two distinct seed lots are included in the trials.

Teagasc is also carrying out work in this area. In 2014 Teagasc started a four year project, working with researchers in Lithuania and France, with the aim of procuring individual trees of ash which show resistance/tolerance to the disease. If successful these trees will then be used to bulk up stocks of resistant trees, as well as for establishing seed producing orchards with resistant parent trees. This work is being funded from within the Department’s normal subvention to Teagasc.

The Department is closely following similar work in Denmark, which is further advanced, and where it is understood over 100 ash trees have already been selected which are tolerant to Ash Dieback disease in Denmark and whose progeny also display high levels of tolerance. The Department is also monitoring efforts by researchers in other European countries, for example Austria and Germany, who are actively seeking to identify trees exhibiting a similar tolerance and develop a deeper understanding of the interactions between the pathogen and host.


Modelling Ash Dieback

The Department has provided research funding through the CoFoRD forest research programme to a UCD-led team to model the airborne spread of the Ash Dieback disease. Together with the University of Cambridge and the Department's Forest Service, this applied project aims to assess the risk of ash dieback spread into and across Ireland. Airborne dispersal of fungal spores is an important mechanism for the spread of this disease. This modelling research will predict the extent and spread of fungal spore plumes from known infected sites by combining climate data from Met Éireann and the latest information on the disease. This information will be fed into the UK Met Office's atmospheric dispersion model. The model was originally developed in response to the Chernobyl accident in 1986 and has since been developed into a sophisticated tool for simulating atmospheric dispersion events more generally.


Ongoing policy review

Within the framework of the All-Ireland Chalara Control Strategy of July 2013 a comprehensive review of policy options in relation to the disease is currently being undertaken by officials from the Department and DARD in Northern Ireland, further to the results of the summer surveys undertaken in both jurisdictions. This review of policy options will focus in particular on the development of a new strategic approach to the disease, including a review and updating where required of the delivery mechanisms such as the Reconstitution Scheme.


Legislation - Initial national measures - 2012

In November 2012, legislation was put in place to restrict the movement of ash seeds, plants, or wood into or within the country with a view to preventing the establishment of the disease on the island. This legislation was by way of an Order (S.I. No. 431 of 2012) made under the Destructive Insects and Pest Acts 1958 and 1991. Similar legislation was introduced at the same time in Northern Ireland and in Great Britain.


Legislation - Update of legislative measures - 2015

In May 2015, the Department in consultation with DARD, commissioned the author of the original PRA to re-examine the risk associated with ash wood as a pathway for the disease in light of any new research in the intervening period and to supplement the Pest Risk Analysis (PRA) - Pest Risk Analysis for Hymenoscyphus pseudoalbidus for the UK and the Republic of Ireland – by means of an addendum. Dr. Sansford’s report was received on 14th August September 2015. Amongst other things, it found a lack of scientific evidence to link large diameter ash wood with the lifecycle of the disease. 

Arising from the findings in Dr. Sansford’s report the Department and DARD officials agreed that relaxing certain legal measures restricting ash wood imports would not impact on the control of the disease. On 3rd November 2015 the Minister for Agriculture, Food and the Marine updated the legislation on the importation of ash wood into the country.

The new Order (S.I. No. 479 of 2015) restates the provisions contained in the previous Order (S.I. No. 431 of 2012) as they pertain to plant and plant products (and which remain common to both jurisdictions) but introduced a number of changes in relation to the documentary requirements around the importation of ash wood as well as the required pre-importation treatments.


EU Plant Health law

Ash dieback is not regulated in any Member State under the EU Plant Health Directive (Council Directive 2000/29/EC). 

In taking action to control plant diseases, Ireland like all other EU Member States must comply with EU plant health legislation including when the organism is not specifically regulated.  Notice of the 2012 legislation and other emergency measures then being taken by the Department were notified to the European Commission and the other Member States beforehand and over the past three and a half years the Department has kept the EU Commission and the Member States informed of its actions.

In order to justify the continuation of such legislative restrictions, which otherwise may be deemed by the European Commission to be unjustified barriers to the free movement of goods (plants and plant products) within the internal market, authorities in both Ireland and the UK (which has near comparable legislative restrictions) had to produce to a Pest Risk Analysis (PRA) report which reflected the current status of the pathogen from surveillance in their respective territories.

Acting in concert with the Department, the UK Forestry Commission produced a PRA report to cover the territories of both jurisdictions in May 2013. The PRA examined additional pathways of entry (seeds, airborne ascospores) and all potential pathways (plants, wood, seeds, soil/growing media, airborne ascospores) are examined in depth. A more detailed consideration of pest risk management options was also undertaken, with suggestions for future controls and a list of uncertainties with associated research needs provided.

In January 2015, Ireland and the UK gave a detailed presentation to the European Commission on their respective actions taken to date and future plans relating to the disease. Ireland will continue to provide periodic updates to the European Commission as and when required.


Reporting Suspect cases

Forest owners, forest nursery staff, and members of the public are asked to be vigilant for the disease and report (with photographs, if possible) any sites where there are concerns about unusual ill health in ash, to the Forest Service, Department of Agriculture, Food & the Marine, by e-mail or by phoning 01-607 2651.

Nursery stock producers should direct queries to your local Plant Health Inspector immediately. Alternatively, queries can be sent by e-mail to, by fax to 01-627 5994, or by contacting the Department’s Offices on 01-505 8885. Reports will be followed up by relevant staff from the Department.


TreeCheck App

In April 2015 Minister of State Tom Hayes and Minister Michelle O’Neill MLA launched an All Ireland smartphone ‘App’, called TreeCheck, which allows members of the public to report suspected cases of disease or insect attack of any tree species. Using a GPS-enabled smartphone the location of the suspect tree may also be recorded by the app to allow a follow-up inspection by Inspectors in the relevant jurisdiction if required. It is hoped that this App will help not only with regard to the early detection of new occurrences of Ash Dieback disease but also other possible pest and disease outbreaks.

All reports received will be acknowledged and those of particular concern taken forward for follow up by specialist plant health inspectors.

To access the TreeCheck App scan the attached QR with your smart phone or type the address into your mobile web browser. (It is not available in the App store.) You will be presented with the App and the option to save a link to your home screen. Follow the directions for your phone.  Please note if you have a GPS enabled phone you may be asked to “Share Location”. Choosing to share your location enables us to have accurate geo-location data to assist our Inspectors in the event we need to investigate your report further“


added 289.01.16

Practical measures to avoid the spread of Ash Dieback

In terms of avoiding the potential for further spread of the disease, before leaving a forest where ash trees are present, landowners and other visitors are advised to remove all plant debris such as leaves etc. from clothing and footwear. Plant material should not be removed from such sites and where the presence of the disease is suspected the following hygiene measures should be observed:

  • Footwear: Wash off all plant and soil debris from boots. Spray your boots with disinfectant and dispose of any used water onto an area where the water will not run into a watercourse.
  • Clothing: Check all clothing for any plant material.
  • Tools & equipment: Wash off all plant and soil debris and apply disinfectant afterwards. Dispose of any used water onto an area where it cannot enter a watercourse.


Useful websites

Further and updated information on ash dieback disease can be found on the following websites:


Relevant Documents:

Press Releases to date: