The disease is thought to have been present in the trust's Holnicote plantation in Somerset since 2001, longer than anywhere else in the UK, due to its presence on imported young trees.
Chalara was only confirmed there last month, but only ten per cent of the six thousand ash trees at the site were found to show any signs of the disease.
The trust's natural environment director Dr Simon Pryor said: "Even the trees affected have not suffered as much as we'd have expected, and very few have died, despite apparently having had the disease for nearly a decade.
"Whilst we don't want to be too optimistic on the basis of this one outbreak, this does confirm the view we've held from the outset that it is worthwhile removing infected trees in order to try to slow the spread – especially in places like this so far from the main area of the disease in the South East."
The trust will now ask the Government to look again at its control strategy "which to us does not appear to fit well with current modeling", Pryor added.
Mark Courtiour, countryside operations manager at Holnicote, said that discovering Chalara at the estate was "heartbreaking", particularly as the trust had originally been led to believe that the trees were from British stock.
He said: "We will be felling all the infected trees as a matter of priority and filling the gaps with other species. However, there is a real glimmer of hope and we are continuing inspections at the site."
Meanwhile the number of sites in Ireland where Chalara has been confirmed has now passed 100.
The infected sites range from forestry plantations and hedgerows to nurseries and even garden centres.
The disease was first found in the Republic last October.