Box tree moth quarantine now includes 12 counties in southeast, central Michigan

LANSING — A quarantine to contain an invasive pest has been expanded to include 12 counties in southeastern and central Michigan.

Lenawee and Monroe counties already were part of the box tree moth quarantine. The other counties are Clinton, Eaton, Ingham, Jackson, Livingston, Macomb, Oakland, St. Clair, Washtenaw and Wayne, according to a news release from the Michigan Department of Agriculture and Rural Development. Macomb and St. Clair are the additions to the quarantine area.

Under the quarantine, the whole plant, plant parts and nursery stock of the genus Buxus, including all living and dead material, cannot be moved outside of the quarantined area. Holiday greenery, such as wreaths, boughs, and grave blankets are exempt from this restriction if moved from Oct. 15 through Jan. 1.

Although not a threat to Michigan’s natural resources, the box tree moth can lead to significant defoliation and death of ornamental boxwood, MDARD said.

Infestations were found in November 2022 at two residences in Clinton. MDARD has been expanding the quarantine area since then. The initial quarantine area was established in April 2023 and included all of Lenawee and Washtenaw counties and parts of Monroe and Jackson counties.

“By expanding this quarantine, we hope to keep box tree moth from moving to new areas in the state, while minimizing the impact on Michigan’s horticulture industry,” Mike Philip, MDARD’s bureau director of environment and sustainability, said in the release. “MDARD is working closely with Michigan’s horticulture industry to ensure the safe trade of plant materials, and to minimize the impact on nurseries, greenhouses, and retailers both inside and outside of the quarantined area.”

Box tree moth caterpillars are green and yellow with white, yellow and black stripes and black spots. Adults have white wings with dark brown borders and a distinctive white dot or mark in the middle of each forewing.

Box tree moth may not be easily recognized at the beginning of an infestation, because young caterpillars hide among twigs and leaves. Signs of infestation include chewed, cut or missing leaves, yellowing or brown leaves, white webbing, and green-black excrement on or around the plant. Larvae skeletonize the leaves and feed on the undersides, causing defoliation and dryness and eventually leading to the plant’s death.

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“In the spring, residents within the quarantine area should examine their boxwood for symptoms of box tree moth. Suspected cases should be reported online at Michigan.gov/ReportBTM,” Philip said. “By reporting any signs of the pest, Michiganders can help us determine the scope of the infestation and reduce the spread.”

After MDARD officials have confirmed a suspected case, residents are advised to remove infested branches or, for heavy infestations, cut the boxwood from its base. It should grow back from its roots. All boxwood debris should be double bagged in plastic and discarded with household trash.  Some municipalities or trash vendors may have restrictions surrounding plant material disposal, so residents should check with their local waste management entity for guidance. Michigan State University maintains a list of insecticides known to be effective against box tree moths and other destructive caterpillars. It can be found online at tinyurl.com/MSUmothinsecticide.

— Contact reporter David Panian at dpanian@lenconnect.com or follow him on X, formerly Twitter: @lenaweepanian.