Chalara has now been confirmed in 525 sites across Great Britain since the first case was confirmed last autumn.
A joint statement by the Forestry Commission and Defra said: "As the trees are now in summer leaf,it is easier to see cases of Chalara, and further sites are likely to be identified."
Martin Ward, the UK Government's Chief Plant Health Officer, added: "We expected to see new cases as the leaves came through on ash trees.
"The better informed we are, the more effective we can be in our work to slow the spread and reduce the impact of this disease, and we will beinvestigating this new case closely."
Defra is hosting a summit later this month to discuss a collective response to the recommendations made in the report by the independent Tree Health and Plant Biosecurity Expert Task Force published in May.