The Hemlock woolly adelgid's march into northern forests has struck the Lake George area of the Adirondacks, the state Department of Environmental Conservation reported.
It's the Adirondacks' first known infestation by the small insect, which is native to East Asia, the DEC said in a statement.
DEC Commissioner Basil Seggos said the agency surveyed 250 acres of Adirondack forest and found only one other tree near the original discovery with a similar infestation.
Targeted insecticides can be used to treat the insect.
The Hemlock woolly adelgid infests hemlocks by feeding on twigs, eventually killing the trees.
DEC officials say the public can help by reporting suspected infestations online.
Small infestations were confirmed in Erie County and Cattaraugus County in 2015, according to the DEC.