Safeguard against spreading the invasive box tree moth
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EmailHave you noticed heavy box tree moth damage on your boxwoods this season? Here's what you need to know about safely disposing of infested plants.
Boxwoods are a beloved staple of formal landscapes, hedges and foundation plantings across the United States. But a destructive pest—the invasive box tree moth (Cydalima perspectalis)—is threatening the health and longevity of these ornamental shrubs continuing to be a part of Michigan’s landscape.
Already causing serious damage in Europe, the box tree moth has the potential to devastate one of the most widely planted shrubs in the U.S. In parts of Europe, boxwood hedges with heavy infestations have been completely defoliated in just a few weeks. In colder regions like Michigan, severe defoliation can happen within a few months in heavily infested areas. In places with lighter infestations, defoliation may take a couple of years, but it will still occur if no treatments are used to manage the pest.
Early detection and responsible management are key to protecting boxwoods in our landscapes. For more information about Michigan’s quarantine zone, treatment options and more, visit Michigan State University Extension’s box tree moth website.
Life cycle and identification
The box tree moth goes through several life stages—egg, caterpillar, pupa and adult—and is known to have two to three generations per season in Michigan (1.5-2.5 generations are predicted in northern Michigan and 2.5-3.5 generations in southern Michigan).
Adults are typically white with a brown head and abdomen, with white wings outlined in a thick brown border. Some adults may be completely brown with a small white streak on each wing, though this morph is not as common and has not been reported in North America to date. Both color forms can appear in males and females. They live about two weeks and are active from spring through fall, with generations overlapping.
Eggs are pale yellow, laid in flat, jelly-like clusters on the undersides of boxwood leaves. They hatch in about three days.
Caterpillars, the most damaging stage, are greenish-yellow when young with black heads. As they mature, they develop thick, black and thin, white stripes along their bodies, with white-outlined black dots. Mature caterpillars can reach 1.6 inches long. They overwinter inside silk webbing attached to boxwood leaves and can survive temperatures as low as -22 degrees Fahrenheit.
Pupae are initially green with black stripes, turning brown as they mature. Pupation begins in spring and continues throughout the summer into fall.
Feeding begins in early spring and can extend into October, depending on temperature. Caterpillars tend to feed in sheltered parts of the plant, spinning webbing and hiding deep in foliage, making early infestations difficult to detect (see Photos 1 and 2).
Damage done: How box tree moth harms boxwoods
The larvae feed aggressively on boxwood leaves, often leaving only the leaf midrib behind. Over time, this defoliation can give plants a scorched or browned appearance (see Photo 3). In severe cases, caterpillars may also chew on the bark of stems, girdling them leading to plant death.
Early signs of infestation may include:
- Webbing on foliage
- Leaves with “peeled” appearance, only midrib of leaves remaining
- Scattered green-black frass (caterpillar droppings)
- Dieback and browning from heavy feeding
Without intervention, the damage can escalate quickly, especially during multiple generations of feeding in one growing season.
Monitoring and movement: Catch it before it spreads
The spread of box tree moth can happen both naturally and through human activity. Dispersal distance though natural flight patterns of the moth is estimated to be about 3-6 miles per year, while infested nursery stock can move the pest much further.
To detect the pest:
- Look for signs of damage, especially inside the plant canopy.
- Inspect regularly, especially during active periods from March through October.
In Michigan, box tree moth is a regulated pest with a very limited distribution. If you see it and you are outside of the quarantine area , report it immediately to Michigan Department of Agricultural Resources Department through their Eyes in the Field service. (Clinton, Eaton, Ingham, Lapeer, Livingston, Oakland, Jackson, Washtenaw, Wayne, Lenawee, Monroe, Macomb and St. Clair County residents do not need to report.)
Cultural and mechanical control options
The most effective strategy is early, proactive management:
- Hand-pick larvae from lightly infested plants. Drop them into a bucket of soapy water or freeze them in a sealed bag before disposal.
- Clear away leaf litter and debris in fall, especially around heavily infested plants, to remove potential overwintering sites.
- Keep plants healthy with proper pruning and watering, which can help reduce stress and support recovery from minor damage.
These physical controls are most useful for small gardens or during the early stages of infestation. For chemical recommendations for control, see the Michigan State University Extension article, “What the box tree moth quarantine means for Michigan homeowners.”
Responsible disposal: Don’t spread the pest
If you remove infested plant material:
- Double-bag it in plastic and place it in the municipal waste. If you leave the sealed bag to sit in the sun for several days, this can help ensure that any remaining larvae are killed before disposal.
- Do not compost at home or leave clippings at the curb for yard waste pick-up.
- Collect and discard fallen leaves under boxwoods to remove caterpillars that could overwinter. Since box tree moth overwinters as caterpillars that are attached to boxwood leaves inside webbing, it’s a good idea to remove any debris left behind by the plants that could provide material to overwinter in (see Photo 4).
- If permitted locally, burning or deep burial may also be options—check with your municipality.
- If you are a landscaper, or bring yard waste to a local compost facility, Michigan’s Interior Quarantine stipulates the following: Movement of Buxus spp. yard waste (branches and boughs with leaves and twigs attached, or un-composted Buxus spp. yard waste which has been chipped) from locations within the regulated area to any destination inside the regulated area is prohibited, unless it meets both of the following conditions:
- It is moved to a disposal site where there are no Buxus spp. within 100 yards.
- During the high-risk period of March through October, said Buxus spp. yard waste may only be transported when enclosed by a covering adequate to prevent the spread of box tree moth (such as canvas, plastic or closely woven cloth), or is transported in an enclosed trailer body or vehicle.
You must destroy the insect before plant material can be moved. This could include double bagging (see Photos 5-8), chemical treatment or chipping.
Box tree moth is a serious threat to boxwoods in Michigan, but with vigilant monitoring, early intervention and responsible disposal, we can help stop its spread. Whether you're a home gardener, landscaper or nursery professional, your actions matter. Keep a close eye on your boxwoods and take steps to protect one of the most prevalent plants in our managed landscapes.
This work is supported by the Crop Protection and Pest Management Program [grant no 2024-70006-43569] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
