Michiganders battle boxwood pests ravaging shrubs

Invasive leafminers and moths are damaging boxwoods in Michigan
Infestations can kill or damage the shrubs, prompting complaints and quarantines
Annual treatments or planting shrubs resistant to the invasive species could help prevent future infestations

Invasive pests are damaging boxwood shrubs in Michigan, frustrating homeowners and leaving once-healthy plants pale, blistered and dying

They’re called leafminers, and they’ve been destroying boxwoods in places like the Grosse Pointes, near Detroit, where residents are grappling with widespread decline.

“So many people don’t know what’s going on,” said Martha Schroeder of Grosse Point, who told Bridge Michigan she has had to dig up at least three shrubs because “there was no life left in them.”

“It’s sad to see all of these old boxwoods have been eaten up,” she said.

A row of dull-looking shrubs. — The landscaping around numerous homes in Grosse Pointe Park have been ravaged by the boxwood leafminer. (Brian Widdis for Bridge Michigan)

Schroeder first noticed signs of the invasive pest at her home in Grosse Pointe last year and reported it to the state. She spotted them again this year and saw they were attacking her neighbors’ shrubs, too.

The leafminer, native to Europe, is one of the most destructive pests for boxwoods, a popular and slow-growing evergreen shrub commonly used in landscaping.

Leafminers are small orange flies that lay eggs inside boxwood leaves. Once hatched, the maggot-like larvae feed on leaf tissue, leaving shrubs damaged and discolored.

Boxwoods were first introduced to North America in the early 1900s and have since spread widely across the U.S., including Michigan. Some shrubs are more resistant than others, but leafminers have destroyed boxwoods in west Michigan for many years.

Infestations are most visible in spring, when larvae create blistered leaves that, when torn open, reveal tiny, yellow maggots. Adult flies leave pinprick-sized exit holes on the underside of leaves.

Other threats

Michigan boxwoods face another growing threat beyond leafminers: The box tree moth, a new invasive pest that can strip boxwood shrubs of their leaves and even kill them.

Box tree moths have reportedly wreaked havoc in Europe, prompting the Michigan Department of Agriculture and Rural Development in 2023 to implement a boxwood quarantine zone.

A map showing the 13 counties under "quarantine." — The Michigan Department of Agriculture and Rural Development has implemented a “box tree moth interior quarantine” for 13 counties. (Courtesy of MDARD)

The current quarantine zone includes 13 counties in southeast and central Michigan: Clinton, Eaton, Ingham, Jackson, Lapeer, Lenawee, Livingston, Macomb, Monroe, Oakland, St. Clair, Washtenaw, and Wayne.

People are generally prohibited from moving boxwoods out of those areas in order to limit the potential for spreading the moths. Once boxwoods “are infested with this pest, it is difficult to eradicate,” according to the order.

The first sign of the boxwood-killing moth is usually bare leaves caused by caterpillars eating them. These caterpillars are lime green with black stripes, white spots, tiny hairs and a shiny black head.

As adult moths, they can be light or dark but always have white spots on their front wings. They are most active from June to October but can be found all year.

“When the caterpillar feeds on the leaf, it’s going to chew that leaf away,” said Sarah Hughson, an insect diagnostician at Michigan State University. “You’re going to see just a partial leaf or you’re going to see no leaf.”

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Caterpillars also create webbing and leave droppings on the leaf.

Leafminers, meanwhile, are “going to produce the yellow or orange blistering on the leaf and the leaf is going to be whole,” Hughson said.

How to protect your plants

A close-up of boxwood leafminer. — Invasive pests like the boxwood leafminer and box tree moth are spreading across Michigan, leaving once-healthy shrubs discolored, defoliated and in some cases dead. (Courtesy of Daniel Herms, Ohio State University)

Annual feeding can disfigure shrubs as leaves drop in midsummer. Repeated infestations may cause defoliation and leave plants more susceptible to drought and disease.

“One of the best things you can do is choose boxwood varieties that are less susceptible to the insect,” Hughson said.

The most effective way to control boxwood leafminers is with yearly insecticide treatments, though success depends on carefully timing applications with the emergence of adult flies.

“The adults will be out during the late spring, early summer period but the larvae will be inside the leaf for the rest of the year,” she said. “They spend most of their life inside the leaf. Even though you’re not seeing the flies, they might still have larvae inside the leaf.”

In cases of heavy infestation, removing the affected shrubs could be the only solution.