The finding is a first for Ireland. Horticulture Week revealed the disease was in the UK in June.
The Department is working with the site owner involved to destroy the material and remove the risk of the disease spreading.
The Department is also investigating a number of other sites planted with imported ash trees from the same consignment which originated from continental Europe.
Emergency measures under the Plant Health Directive are to be introduced. The measures being introduced under Statutory Instrument will require that any ash plants imported into the country would come from an area known to be free of the disease. This would be regulated under the EU Plant Passport system.
The Department is also calling on the forest nursery trade and contractors to introduce a voluntary moratorium on imported stock from continental Europe with immediate effect.
Officials at the Department have recently met with their counterparts in Northern Ireland to co-ordinate an all island approach to tackling the disease. Department officials are also working closely with the relevant authorities in Great Britain.
Forest owners and members of the public are asked to report any sites where there are concerns about unusual ill health in ash to Forest Service, Department of Agriculture, Food and the Marine by email email@example.com or by phoning 01 6072651.