Alan

Yes, Box Tree Moth (BTM) is a serious pest of boxwoods. It is an invasive pest native to East Asia. In Ohio, BTM infestations cause rapid, severe defoliation. Because BTM produces multiple generations per year (with overwintering caterpillars emerging in early spring), populations ramp up quickly.

But BTM doesn’t spell the end of boxwoods. There are effective controls for the BTM that stop this pest from destroying boxwoods.

About the insecticides you asked, some are effective against the BTM, and others are not. Sevin (carbaryl) and Cross-Check (Bifenthrin) are effective against BTM. However, both are broad-spectrum insecticides that can harm many beneficial insects. Imidacloprid is not effective against BTM.

Btk (Bacillus thuringiensis subsp. kurstaki) is a recommended, highly effective control for BTM. Btk is a natural biological insecticide produced from soil bacterium that specifically targets the digestive tracts of caterpillar larvae. It is non-toxic and safe for humans, pets, birds, and beneficial insects like bees and lady beetles. Caterpillars eat leaves treated with Btk. Once ingested, the bacteria stop the caterpillars from feeding within hours, and they die in a few days.

Always read and follow the directions on the insecticide label for the most effective and safest application.

Also, you may consider using a professional pest control company.

BTM caterpillars attract several insect predators such as yellow jackets and assassin bugs that help control BTM numbers. These beneficial insects can be harmed by broad-spectrum insecticides.

When should control be applied? First preventative applications (spraying) for BTM should not be done. BTM has several generations in a year, so there is no single best time to treat. Instead, monitor your boxwoods for BTM caterpillars. BTM caterpillars like to feed from inside out, so look in the interior of boxwoods as well as the outside. Begin monitoring in late April to early May. And continuing periodic monitoring during summer and into fall. Look for the caterpillars (they can be different sizes) or signs of fresh chewing. Treat the boxwoods if BTM is found.

The Ohio Department of Agriculture tracks the spread of BTM in Ohio. You should report any BTM finding to ODA. The ODA has a website to report BTM and other pests.

While BTM can cause damage to boxwoods, boxwoods can recover. There are effective controls for BTM that prevent the loss of boxwoods. Research is ongoing to develop resistant boxwood varieties.

Thank you for your question. Here are some factsheets with more information on BTM.

BYGL BTM

Management Options

ODA Reporting Website