The news came as professionals were waiting for details of an impending government ban on ash imports, due to be released today.
The Trust is carrying out further investigations at other sites.
it said the time has come for an emergency summit to agree action to tackle the problem of tree diseases, before we lose another native species for good.
Woodland management head Andrew Sharkey said: "Losing ash within the UK landscape would have serious implications to both the ecology, culture and landscape of our countryside.
"This is yet another example of why the protection of our native trees, natural resources and eco-systems needs to be at the top of the agenda and we need a step change in the level of importance placed on bio-security to tackle the bigger issue.
"The occurrence of tree diseases in the UK is becoming far too frequent and once they are established we are often powerless to act.
"We are potentially facing the ash equivalent of Dutch elm disease, and unless we take serious measures as a country we will continue to see problems arising from imported diseases.
"If this was a case of foot and mouth there would be immediate emergency measures put in place to deal with it. We need an emergency task force or summit set up by Government immediately to help deal with current threats and to stop any future threats before they arrive in the UK. We must focus our minds, time, and resources towards these issues and the Government has to act on its own Action Plan for Tree Health and Plant Bio security plan which states that protecting the UK through import controls is a priority."