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Ash Dieback Disease

Ash dieback is a serious disease of ash trees caused by the fungal pathogen Hymenoscyphus fraxineus (previously known as Chalara fraxinea).

Update on Republic of Ireland figures:

Number and location of confirmed findings of Ash Dieback disease in the Republic of Ireland (as of 31 July 2017)

Number by site type / county

Number of confirmed findings (Oct '12 - Dec '15)

Number of additional findings confirmed in 2016

Total as of 31 December 2016

Number of additional findings confirmed in 2017 (up to 31 July 2017) 

Forestry plantations 115 207 322 621
Commercial nurseries 25 3 28 0
Garden centres 4 0 4 0
Private gardens 7 1 8 0
Farm  / agri- environment plantings 25 3 28 0
No. of counties with hedgerow findings 12 5 172 0
No. of counties with roadside / motorway findings 13 1 143 0
  1. There are currently 384 forestry plantations with positive samples distributed over 24 counties: Carlow, Cavan, Clare, Cork, Dublin, Galway, Kildare, Kilkenny, Laois, Leitrim, Limerick, Longford, Louth, Mayo, Meath, Monaghan, Offaly, Roscommon, Sligo, Tipperary, Waterford, Westmeath, Wexford and Wicklow.
  2. There are currently 17 counties with individual positive samples taken from trees in native hedgerows: Cavan, Clare, Donegal, Galway, Kildare, Kilkenny, Leitrim, Limerick, Longford, Mayo, Meath, Monaghan, Roscommon, Sligo, Tipperary, Wexford, and Wicklow.
  3. There are currently 14 counties with individual positive samples taken from trees in roadside / motorway landscaping plantings: Clare, Cork, Dublin, Galway, Kilkenny, Limerick, Laois, Louth, Meath, Monaghan, Offaly, Tipperary, Waterford, and Westmeath.

What is it?

Ash dieback is a serious disease of ash trees caused by the fungal pathogen Hymenoscyphus fraxineus (previously known as Chalara fraxinea). It has spread rapidly across much of Europe. It was first noted in Republic of Ireland in October 2012 on plants imported from continental Europe. The disease can affect ash trees of any age and in any setting. The disease can be fatal, particularly among younger trees.

What does it look like?

The wide range of symptoms associated with ash dieback includes:

  • Necrotic lesions and cankers 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
  • Brown / orange discolouration of bark

Further information:

Foliage wilt Shoot dieback Elongated angular stem lesions
Note, symptoms similar to the above may be caused by other factors, e.g. frost.

How can it spread?

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.

However, movement of larger diameter ash logs from infected areas is considered to be much lower risk as long as certain phytosanitary measures are properly implemented. These include ensuring the larger diameter logs 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.

What to do?

Forest and land owners are asked to be vigilant for the disease and to report (with photographs, if possible) any sites where they have concerns about unusual ill health in ash, to the Forest Service, Department of Agriculture, Food and the Marine: by email (forestprotection@agriculture.gov.ie); or, by phone (01-607 2651).

Please do not remove any plant material from a site containing suspect trees. Also, please observe the following hygiene measures on sites where the disease is suspected or where an ash survey is being carried out to help avoid its potential spread:

  • footwear: wash off all soil and plant 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; and,
  • tools and equipment: wash off all soil and plant debris, and disinfect and dispose of any used water onto an area where the water will not run into a watercourse.

When visiting a forest:

  • do not remove any plant material from the site; and,
  • clean clothes and footwear of any plant material, including leaves, before leaving the forest.

Please highlight this serious disease by downloading and displaying this Chalara Warning Poster (2.5 MB) in a prominent place.

Chalara in Europe

Department of Agriculture Updates: