Hemlock woolly adelgids have been found in southern Mason County, the Michigan Department of Natural Resources says.
Infestations were previously found in Allegan, Ottawa, Muskegon and Oceana counties.
Hemlock woolly adelgids are small insects that use their long, siphoning mouthparts to extract sap from hemlock trees. Their feeding weakens needles, shoots and branches. Without treatment, infested trees die within four to 10 years.
This spring, crews wil focus on treated infested trees to prevent hemlock woolly adelgid from spreading further north.
There is an internal quarantine in place for Allegan, Ottawa, Muskegon and Oceana counties. The quarantine restricts the movement of hemlock nursery stock and unprocessed hemlock products.
Late fall through early spring is the best time to check hemlock trees for the presence of hemlock woolly adelgid. The DNR says to look on the undersides of branches for evidence of round, white ovisacs near the base of the needles. Ovisacs look like balls of spun cotton.