The CLA today (2 November) urged its members and all tree owners to get out into the woods this weekend to look for cases of Chalara fraxinea in ash trees before any more leaves fall.
The Association is working closely with the Forestry Commission to compile a spotter's guide to help woodland owners identify the symptoms of ash dieback and record the spread of the disease on a national database.
CLA President Harry Cotterell said: "The Environment Secretary has specifically asked CLA members to get out this weekend to check on whether their ash trees have Chalara. He wants to get a more accurate feel of how widespread the problem is.
"Cases need to be identified within the next 48 hours before any more leaves fall. Once the leaves have gone, the fungus is much harder to detect."
The Forestry Commission's guide to identifying the disease explains that the most obvious symptoms of Chalara fraxinea are blackened leaves and necrotic lesions on the twigs, branches and main stem.
Tim Rollinson, Forestry Commission Director General, said: "We all take the threat to our ash trees extremely seriously and would like to thank the CLA and its members for all their efforts and we will continue to work closely with them."
Owners can check if their trees are showing signs of ash dieback by following the advice at www.forestry.gov.uk/chalara and downloading and completing a survey form from http://www.cla.org.uk/ty/nDYcRg/.