These life stages of box tree moth were on display at the Delaware Horticulture Industry Expo. TM caterpillars are green and hairy, with black stripes and white dots. They may be seen on boxwood leaves as early as March. (Photo by Carol Kinsley)
There’s a new invasive pest from Asia attacking a popular ornamental evergreen shrub in the United States, the boxwood (Buxus spp.)
The box tree moth (Cydalima perspectalis), completes its development mainly on boxwood. Capable of spreading 100 miles in a year, the BTM is now widespread in Europe. It was found in Ontario, Canada, in 2018 and confirmed in New York in 2021. It has since spread to several other states and was first detected in Delaware in 2024 and Maryland in July 2025.
“We first found BTM in a private yard in Little Creek. We had expected to find it in a nursery first, but did not,” said Stephen Hauss, Delaware Department of Agriculture’s environmental program manager, during the Delaware Horticulture Industry Expo held in January. It has been found on multiple properties around East Dover since then, and in Smyrna, he added.
In Maryland, the moth was first confirmed in a state park in Washington County.
There are no boxwood species native to North America, Hauss said, but many were planted on historical sites long ago, so there’s an emotional aspect when these shrubs are damaged or killed, Hauss said. There is a Buxus sempervirens ‘Suffruticosa’ at Bethel Baptist Church in Wilmington, Delaware, that is more than 150 years old. It is 10.5 feet high and 72 feet in circumference.
Maryland has numerous historic boxwood plantings in Somerset and St. Mary’s counties, along with many 18th and 19th century manor estates on the Eastern Shore.
BTM is now a federally regulated pest with quarantines imposed in some states or parts of states. The Federal Order states: “Boxwood plants may only be moved interstate from a quarantined area from an establishment operating under a compliance agreement, and only if accompanied by a certificate issued by a state agricultural authority certifying that the requirements of this Federal Order and the compliance agreement have been met…. APHIS prohibits movement of all other regulated articles of boxwood, including plant parts, pieces, cuttings, clippings, debris, and any portion of the plant, alive or dead, except for decorative purposes.”
Landscapers will probably be the first to see issues, Hauss said. It is important that they familiarize themselves with the BTM and the signs of its presence. Landscapers will need to communicate best practices to property owners, warn that boxwood may require treatment and suggest it might be advisable to plant something else.
Damaged boxwood leaves may appear “peeled” or only have the mid-rib left behind. Heavily infested shrubs may appear brown, “see-through” or “torched.” Caterpillars produce webbing and hide among leaves and twigs as they feed or pupate. They also consume the bark of twigs when few leaves remain which can kill the plant. They produce green-black frass.
The BTM caterpillars are green and hairy, with black stripes and white dots. They grow to about 1 to 2 inches. Adults are white with a thick brown border on the wings and are active at night. Once boxwoods are defoliated, other hosts could include burning bush (Euonymus alatus,) Japanese spindle (E. japonicus,) or Kashi holly (Ilex chinensis).
Caterpillars were last seen in Delaware in October, Hauss said, and are expected to resume activity once temperatures are above 50 degrees for three consecutive days, which typically occurs in March. Females will lay their overlapping yellowish eggs (5-20) on the underside of boxwood leaves. In the Delmarva climate, the pest may have two to three generations from July to October.
Virginia and Kentucky are trying to eliminate the pest. Hauss noted it has not been eradicated anywhere that it was introduced in Europe.
“Eradication is not an option in Delaware,” he said.
Delawareans can help prevent BTM from spreading by monitoring and controlling infestations. Remove infested boxwood plant branches. For heavy infestations, cut the boxwood from its base. The plant should grow back from its roots.
All boxwood debris should be double bagged in plastic and placed in the trash. Homeowners should follow the University of Maryland Extension’s pesticide recommendations. According to UME, Unnecessary treatments can harm beneficial insects and cause secondary pest outbreaks.
With small infestations, hand-pick or prune caterpillars off plants and place them in a bucket of soapy water.
For large infestations, UME recomends using a horticultural oil or insecticidal soap spray on small caterpillars, following all label instructions. Adequate coverage is needed for effective control, aiming for the underside of leaves (where the young caterpillars feed). A professional pest control company can be contacted for further guidance.
Heavily infested plants may need to be removed and destroyed to prevent further spread, UME said.
A long-term solution is also underway. The American Boxwood Society, a not-for-profit membership organization devoted to the appreciation, scientific understanding and propagation of boxwood, has partnered with Saunders Brothers nursery in Virginia to develop varieties resistant to boxwood blight and the BTM.
NewGen ‘Independence’ is one. It has a classic look, strong branches and is a good replacement for English boxwood. A “fast, easy grower,” ‘Independence’ will reach 3.5 feet by 3.5 feet in 15 years.
Other resistant cultivars include Buxus microphylla ‘Little Missy’, ‘Winter Gem’ and ‘Green Beauty’ as well as B. harlandii and B. sinica.
“Boxwood has been around since the 1400s,” said Jesse Armer, a horticulturist at Longwood Gardens and owner of Holly Oak Horticultural Services in Kennett Square. “It’s not going away.”
