Help needed from Michigan residents: Protect America’s boxwood from invasive caterpillar
Box tree moth will destroy most boxwood shrubs in the country if it becomes established. Michigan residents can assist in the early detection trapping program.
On May 28, 2021, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) announced that they confirmed the presence of box tree moth, Cydalima perspectalis, in the continental United States and are working to contain and eradicate the invasive pest. The infested boxwood has been removed and surrounding host-material has been treated. Caterpillars of the invasive moth, native to east Asia, first consume the leaves and then the bark of the plant, thereby killing the shrubs. The box tree moth was first accidentally introduced in 2007 in Germany and since then has destroyed an estimated 75% of boxwood shrubs in Europe.
To our knowledge, the box tree moth is not established anywhere in Michigan. However, we are asking residents who have purchased boxwood plants in 2020 or 2021 to check them for signs of infestation and any suspected damage. In Michigan, the moths are expected to complete two generations between June and October, so quick action is essential to prevent this pest from establishing itself in our country. While it is very unlikely that boxwoods purchased this spring were infested, please help protect America’s boxwood plants and be part of this outreach and eradication effort! How? Know the signs of the box tree moth caterpillar and damage and volunteer to hang a trap in your yard!
Signs of the box tree moth
Box tree moth caterpillars only feed and reproduce on boxwood (Buxus spp.). First, you will see the beginning of defoliation of the boxwood leaves (Photo 1). If you begin to see signs of damage, check the boxwood plants for caterpillars (0.25 inches after egg hatch to 1.5 inches long when mature), which are lime green with black stripes and have white spots and hairs (Photo 2). The caterpillars have a shiny black head. As feeding progresses, caterpillars eat the leaves and bark, leaving only the midribs of leaves (Photo 3). With extensive feeding damage, you will see webbing from caterpillar silk and the eventual death of the plants.
How you can help: Early detection through trapping
Michigan State University Extension is partnering with the Michigan Department of Agriculture and Rural Development (MDARD) and the USDA APHIS to implement an early detection program for box tree moth throughout Michigan. The box tree moth was detected at three locations this spring, but MDARD and APHIS have removed the threat in those locations. By working with homeowners throughout Michigan, we seek to learn if the box tree moth has been introduced elsewhere in Michigan. How can you help?
We are seeking Michigan homeowners who have purchased and planted boxwoods in 2020 and 2021 to help us set pheromone traps to determine if the boxwood moth is present in Michigan. The pheromone traps have proved to be very effective for attracting male box tree moths in Europe. Please note that attracting male moths will not cause infestations because the female moths need to be present to lay eggs. The traps mimic the pheromones females emit so they can find a mate. Consequently, the pheromone traps only attract males. If you hang traps on your boxwood, rest assured, you will not be causing a new infestation. You will only be detecting whether box moths are already there.
The adult moths are distinctive and have both a light morph (iridescent white wings with brown border, brown body [Photo 4]) and a dark morph (brown body and wings with white forewing spots [Photo 5]).
An excellent publication, “Box Tree Moth and its SE US Lookalikes,” published by the University of Georgia and Clemson Cooperative Extension, shows the box tree moths and those that may be similar. If you believe you’ve detected the box tree moth, please email photos to the box tree moth team at MSU Extension at email@example.com for positive identification.
Please be aware that at this point we must notify USDA APHIS of any positive finds of box tree moth in Michigan. If caterpillars or moths of box tree moth are found, it is likely that infested plants will need to be treated or removed, and preventive treatments of boxwoods in the area may be initiated. We sincerely hope that we do not find any in Michigan, but if we do, early detection is our best chance of preventing establishment and spread.
Box tree moth team contacts to obtain traps
If you are willing to hang a box tree moth pheromone trap on your property, please fill out the survey below to determine which county MSU Extension office is closest to you to pick up a trap. Each team member has a limited number of PHEROCON IIB BTM Kits for cooperating citizens. Another option is contact the only distributor of box tree moth pheromone traps in Michigan: Great Lakes IPM. Cooperators can learn how to use their kits by watching this instructional video.
Protecting your boxwoods
If you purchased boxwood during 2020 or 2021 and suspect there could be box tree moths or unexplained decline in your boxwoods and you desire to protect your shrubs, we recommend spraying boxwood shrubs twice this summer—in late July and early September—with bifenthrin (several ready-to-use products available at the garden center) or any pyrethroid insecticide for homeowner use. Pyrethroid insecticides are those where the active ingredient ends in thrin, for example cyfluthrin, permethrin, resmethrin, cypermethrin, lamba-cyhalothrin, sumithrin.
Alternatively, homeowners can also spray a Bacillus thuringiensis (Bt) product once every two weeks. Bt is a bacterium that kills insects when ingested. There are subspecies of Bt that affect specific types of insects; kurstaki is the subspecies that specifically targets caterpillar larvae. Look for product labels that say Bacillus thuringiensis subsp. kurstaki (Btk).