The CLA has urged the public to look for cases of ash dieback and is working with the Forestry Commission to compile a spotter's guide.
Chalara fraxinea is just one of a number of deadly diseases that threaten the UK's native trees.
"Cases need to be identified within the next 48 hours before any more leaves fall" said CLA President Harry Cotterell.
"Once the leaves have gone, the fungus is much harder to detect."
Environment Secretary Owen Paterson told delegates at the inaugural National Forestry Stakeholder Forum earlier in the week that he had made addressing tree pests and diseases an 'absolute strategic priority'.
Paterson had specifically asked CLA members to check ash trees for Chalara and said he wanted "to get a more accurate feel of how widespread the problem is".
Professor James Brown, President of the British Society of Plant Pathology, said: "The appearance of ash dieback in British woodlands should be a wake-up call to the government and industry."
"New diseases threaten our woodlands and our food crops. Plant pathology education in Britain needs to be revived, to reverse the decline in expertise and to give farmers and foresters better ways of controlling these diseases."
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."