The pathogen, which kills rhododendrons, oaks and beeches, was found at National Trust for Scotland's Brodick Castle & Country Park on Arran last week.
Trust head of gardens and designed landscapes services Jan Haenraets said: "This is a potentially dangerous disease for our plant life and we will continue to work with experts, including the Scottish Government, to minimise its impact on Brodick.
"Brodick will remain open to the public but it's vital to clean your boots thoroughly after leaving, keep dogs on a short leash during your visit and don't take any cuttings."
Gardeners were advised to look out for signs of the disease.
Earlier this month the National Trust for Scotland and Royal Botanic Garden, Edinburgh, brought specialists and gardeners together to discuss dealing with P. ramorum.