The finding follows the first outbreak of the virulent disease in Britain last December, at Balloch Castle Country Park, on the banks of Loch Lomond.
The Forestry Commission is urging all owners of Lawson cypress trees to inspect them regularly for P. lateralis, and report any unexplained symptoms of dieback to its Tree Health Diagnostic & Advisory Service.
Head of the Forestry Commission’s plant health service John Morgan said: "We’ve been on high alert for P. lateralis since it was first discovered at Balloch last year, and we feared it might turn up elsewhere. Sadly, this has proved to be the case.
"The key to containing and controlling it is constant vigilance by tree and woodland owners and managers, and reporting any unexplained dieback to Lawson cypress to us so that we can take quick action to limit the possibility of it spreading."
The Forestry Commission’s Tree Health Diagnostic & Advisory Service can be contacted via firstname.lastname@example.org or by phoning 0131 445 2176.