The island banned the importation of ash trees at the end of last month, and the disease was found on recently imported ash trees in the south east of Guernsey.
All 86 trees in the consignment have been removed and destroyed.
At this time of year, when the trees are bare, the disease can be spotted by diamond shaped lesions on the stem.
Jersey also imposed an indefinite ban on the importation of ash trees at the end of last month after Ash dieback disease, caused by the Chalara fraxinea fungus, was found in parts of England and Scotland.
