Ash Dieback & Horse Chestnut Moths



There are a number of diseases around which devastate trees and shrubs. Some, like the Sclerotinia fungus, which decimates Griselinia hedges is, as far as I am concerned, manna from heaven. Anything that will clear the suburbs of that horribly, nasty, shiny green-leaved bore of a plant is good news. There are a couple of very serious threats to our forest and decorative trees however that are extremely worrying and could be as catastrophic as Dutch Elm disease was in the late 1970s and 1980s. One affects the beloved horse chestnut and the other our native ash. You have probably heard a lot about Ash Dieback disease already. But to recap, this is a serious disease of the Ash (Fraxinus species) caused by a nasty fungus, Hymenoscyphus fraxineus affecting trees of any age in the wild, gardens and plant collections. The disease can be fatal, particularly among younger trees and leaves older trees looking very depressed indeed.   Ash is such a common tree in Ireland that there is great potential for this disease to forever alter the appearance and biodiversity of our hedgerows and woodlands. It is important to spot the symptoms of Ash Dieback early, and if you find an infected tree, it will need to be felled and burnt immediately. As a precaution don’t ever use the leaves of ash to make leaf-mould. If you have ash in your garden, try and collect and burn all fallen leaves. Symptoms to look out for are as follows:

  • Leaves which wilt during the summertime, turning black.
  • shoots die from the tip back to a branch
  • open wounds where a stalk meets the main stem of saplings
  • leaf discolouration and loss

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 e-mail or phone (01-607 2651).

The threat to horse chestnuts is the eponymous horse chestnut leaf-mining moth (Cameraria ohridella). The moths feed on the leaves of trees, turning them brown and causing them to drop in the late summer. Infested leaves are often brown and appear quite dry and make trees look very unsightly.

Although infestation itself does not kill the trees, it can weaken the tree’s immune system and make it vulnerable to other diseases, including bleeding canker, a bacterial disease that creates unsightly leaking lesions on the trunk.

If you spot the moths or their caterpillars on trees, or suspect you may have an infestation would love to hear from you and you should also contact the Department of Agriculture your local plant health inspector or contact:  The British Conker Tree Science project is urging people to record sightings of moth-infected trees on its website to help track the spread of disease.

For further information, visit: and



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