Boxwood Drama: When Your Shrubs Get Munched and What to Do About It

If you grow boxwood in southern Ontario, chances are your shrubs have already joined a very exclusive club: Plants That Have Met the Box Tree Moth.
Don’t worry—you’re not a bad gardener. You didn’t forget to water. You didn’t anger the soil spirits. This moth is now widespread, very hungry, and has absolutely no manners.

The box tree moth overwinters as tiny larvae tucked inside webby leaves, like teenagers refusing to leave their rooms. When spring warms up, they come out snacking, and by May–June you may notice leaves looking skeletonized or suspiciously see-through. In southern Ontario, these caterpillars usually throw two big feeding parties: one in late June–July and another in late August–September. If they eat repeatedly and start chewing stems, boxwood can actually die—dramatic, I know.

Enter: Pheromone Traps (aka Moth Gossip Lines)

Pheromone traps don’t kill the problem outright, but they’re fantastic for spying. These traps attract male moths, helping you figure out when moths are flying so you know when caterpillars are about to show up. Hang one or two traps around boxwood from about May 1 to late September, roughly at shrub height. Check them weekly. Think of them as your garden’s early warning system—not a full security team.  Traps here https://naturalinsectcontrol.com/product/boxwood-moth-trap-lure/

BTK: The Caterpillar-Specific Superhero

When larvae are actually feeding, that’s your cue for BTK (Bacillus thuringiensis kurstaki). This biopesticide must be eaten by caterpillars to work, so spraying without larvae present is about as useful as yelling at squirrels. The good news? Boxwood rarely hosts other caterpillars, so BTK has minimal impact on pollinators and beneficial insects. Win-win.  BTK here https://naturalinsectcontrol.com/product/btk-bacillus-thuringiensis-var-kurstaki-for-caterpillar-control/

In Ontario, homeowners usually spray BTK:

• Early May–mid June for the first larvae
• Mid July for round two
• Late August–mid September if fresh feeding appears

Spray thoroughly—inside dense hedges too—and repeat every 5–7 days while larvae are active.

Neighborly Advice (From Someone Who Chats With Shrubs)

Inspect your boxwood regularly. Hand-pick larvae or spray BTK when numbers are low. Use traps to guide timing, not panic. And if infestations are severe year after year, consider replacing boxwood with a non-host shrub. It’s not giving up—it’s strategic retreat.

Gardening isn’t about perfection. It’s about paying attention, laughing a little, and doing your best—preferably while muttering encouragement to your plants.