Beware of the box tree moth

METRO DETROIT — Box tree moths, an invasive species of insects that can defoliate and kill boxwood shrubs, have been detected in Michigan. Experts say it is important to know how to identify them and eliminate them from your backyard.

If box tree moths are found to be inside of boxwood plants, the plant will be killed within a very short period of time, according to Austin Douglas, owner of Ditch the Itch– Poison Ivy and Mosquito Control Services, an ISA board-certified master arborist.

Douglas’ business, located in Goodrich, not only deals with poison ivy and mosquito control. It has transitioned into one that manages “plant health care” dealing with insect and disease management, and tree preservation services.

“It really depends on how many eggs are on the shrubs. If you had one caterpillar, it would take some time for them to really show some damage, but if you had hundreds of eggs that all hatch, your boxwoods could be devoured in less than a week,” he said. “And when I say devoured, what I am really referring to is they would be completely defoliated, so all of the leaves would be chewed up, eaten up, and they would look like brown shrubs.”

When looking for box tree moths within the boxwood and box tree species of plants, it’s important to notice green and yellow caterpillars with white, yellow, and black stripes and black spots, according information presented under the Michigan Invasive Species Program link under the “Environmental” tab at michigan.gov.

Along with the actual insect, its presence can be detected by loose webbing in the area of caterpillar activity, evidence of feeding on edges of boxwood or box tree leaves, white moths with a brown border and distinctive white comma-shaped mark on each forewing, and clusters of five to 20 pale yellow eggs on the leaves of boxwood or box trees, according to the state.

The Michigan Department of Agriculture and Rural Development expanded the interior quarantine for invasive box tree moths as of January 8, 2025, according to the website.

“The quarantined areas include the entire counties of Clinton, Eaton, Ingham, Jackson, Lapeer, Lenawee, Livingston, Macomb, Monroe, Oakland, St. Clair, Washtenaw, and Wayne,” the website indicates. “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.”

Box tree moths are most active during the night and typically mate between April and July. They can remain active until September or October. Douglas said that this is the earliest he has seen active box moths.

“It’s all weather related. Insects hatch based on temperatures, and we have kind of had this strange spring where in certain locations it’s been quite warm early, and so insect activity has, I don’t want to say increased, but it has sped up,” he said.

When a box tree moth is detected, it’s crucial to act fast, according to Douglas, who said that early treatment is the best course of action.

“A homeowner needs to be treating their boxwoods with a product called Bacillus thuringiensis, and that is a bacteria that affects caterpillars,” he said. “As far as the frequency, they should be treated every 10 to 14 days. Now if that doesn’t sound reasonable for a homeowner to do, then I would recommend that they contact a company that can use the products that are going to last longer on the boxwoods.”

The insects are always going to be there, so committing to a boxwood or box tree species of plant can become a lot of work, according to Douglas.

“They are not going away. They do have multiple generations a year, so even if you treat in early May and then you stop later, generations can pop up in July and August, September, etc.,” he said. “So it’s going to be a constant battle for anyone that wants to have boxwoods, and realistically, if you have boxwoods, you should have them on a preventative program.”

Douglas said that if a preventative program is not possible, it’s probably best to think about getting a different kind of shrub variety that is not going to have this issue.

If your boxwoods or box trees are in trouble, there is no need to fear. They can still be revived in about six weeks, according to Douglas.

“If you were slow to perform treatments, and you see that your boxwoods are in trouble, I don’t want people to freak out and think that they have to rip them out, you can bring them back,” Douglas said. “Ideally, we would prefer a preventative treatment so that way we don’t get to that point but generally speaking we can get them to turn around in about six weeks.”

If you do see signs of box tree moths or its caterpillars, it is important to take photos and submit a report through www2.dnr.state.mi.us/ors/Survey/39.

For more information on Ditch the Itch, go to ditchtheitchmi.com.

For more information on box moths and other invasive species visit michigan.gov/inva sives/id-report/insects/box-tree-moth.

A bulletin is also available from the Michigan State University Extension at canr.msu.edu/resources/box-tree-moth-alert.