Hello and thanks for contacting Ask Extension. Yes this is definitely box tree moth damage. I actually see the caterpillar on your first picture. I’ve attached a file with the caterpillar circled in blue. Since Oakland county is in the quarantine zone, you do not need to report this. For homeowners and landscapers, moving any boxwood material is strictly prohibited, including live or dead shrubs, trimmings and debris. Because of this quarantine you probably won’t be able to replace your boxwood with more boxwood. Based on the life cycle of the box tree moth, I don’t believe that they overwinter in the soil, but once the caterpillar turns into a moth they will fly and infect other boxwoods. Since you know that you have box tree moth in your landscape, there are options for control, steps you can take to prevent further spread, and landscape alternatives to consider when replacing damaged or dead shrubs.

For small infestations:

• 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.

If you decide you want to spray to control box tree moth, apply horticultural oil, insecticidal soaps, Spinosad & Bacillus thuringiensis kurstaki (Btk) to control young larvae. Note: several applications may be needed throughout the season to target larvae of multiple, overlapping generations. As the season progresses and moths emerge, Michigan State University Extension recommends an application of bifenthrin (several ready-to-use products available at the garden center) in late July and early September or any pyrethroid insecticide for homeowner use can be used to control all life stages. Pyrethroid insecticides are those where the active ingredient ends in thrin, for example, cyfluthrin, permethrin, resmethrin, cypermethrin, lambda-cyhalothrin and sumithrin.

Alternatively, homeowners can spray a Bacillus thuringiensis (Bt) product once every two weeks. However, Bacillus thuringiensis is not an effective control for larger caterpillars, eggs or adults. 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 target caterpillar larvae. Look for product labels that say Bacillus thuringiensis subsp. kurstaki (Btk). Always follow the instructions on the label.

For heavy infestations, avoid making preventative applications with broad-spectrum insecticides when box tree moth is not present. Insecticide effectiveness against eggs, pupae, and older caterpillars may be low since they tend to be on the undersides of leaves and hidden deep in a canopy of leaves and webbing. To prevent resistance issues, rotate pesticide mode of action. Select products that are least harmful to pollinators and other insects.

For proper disposal of dead or infected plant material:

• Clean up leaf litter and debris to remove potential overwintering sites.
• Double-bag in plastic and place in municipal waste.

Few shrubs offer the compact size, evergreen foliage, and resistance to deer browsing that boxwood offers. However, with the amount of pest and disease pressure these shrubs are now facing, homeowners may opt for plants that will require less maintenance. Consider the following shrubs when replacing boxwoods: Japanese Holly (Ilex crenata), Inkberry Holly (Ilex glabra), Junipers (Juniperus spp.), Yew (Taxus spp.), or Arborvitae (Thuja spp.) These shrubs among others offer similar form and function in the garden. Be sure to consider your local climate, soil conditions, and deer pressure when finding a suitable boxwood replacement. You mention replacing your infected boxwood with Inkberry holly (Gem Box and Strongbox) and this is a good idea although they may not be as deer resistant as boxwood.

Here are some links to articles about the box tree moth. Hope this helps!

Box Tree Moth Alert - Invasive Species

New box tree moth alert for Michigan homeowners and residents, now available in English and Spanish - Floriculture & Greenhouse Crop Production

Safeguard against spreading the invasive box tree moth - Floriculture & Greenhouse Crop Production

What the box tree moth quarantine means for Michigan homeowners - Floriculture & Greenhouse Crop Production

Sorry, forgot to attach the picture.