All the young trees on these sites have been lifted and destroyed as a precautionary measure to tackle the disease.
The disease was also confirmed in North Wales, at a newly-planted site at Glynllifon College, in Gwynedd. The dieback was spotted by an employee and samples sent for laboratory analysis confirmed the presence of Chalara.
A survey of other sites recently planted with ash from known infected nurseries is continuing. It follows the discovery of the disease earlier this month in a small, newly-planted woodland in Carmarthenshire.
Environment Minister John Griffiths said: "The Welsh Government is taking the threat of this disease very seriously and officials are working closely with our partners in the Forestry Commission (FC), Defra, the Food and Environment Research Agency (FERA) and the devolved administrations in Scotland and Northern Ireland on a UK-wide response to the threat it poses.
"Tree diseases do not respect country boundaries and we need to provide a consistent approach to this threat in order to meet the demands of stakeholders and the public and to ensure that our response is co-ordinated and based on the most up to date scientific evidence."