Rejuvenating boxwood plants damaged by box tree moth

August 28, 2020

A boxwood hedge before and after treatment.

Box tree moth (Cydalima perspectalis) is an invasive pest found in urban landscapes within the Greater Toronto Area that selectively feeds on boxwood shrubs. High populations of box tree moth caterpillar may defoliate boxwood plants; in some severe cases this can result in plant dieback. However, most affected plants will still have healthy stems and roots, and the boxwood plant will leaf out and regrow if you follow these steps:

Step 1: Monitor

Monitor boxwood plants for caterpillars from May to August. For what to look for, read: Box tree moth look for these signs this spring.
Report any new sightings of box tree moth.

Step 2: Treatment

To treat caterpillars, an application of Bacillus thuringiensis k. (BTK) is most effective when used twice a year; once in late May and once in late July. For application, please choose a day where rain is not anticipated in the next 24 hours. Hire a professional to administer treatment.

Step 3: Fertilize

Landscape Ontario recommends fertilizing twice – early June and mid-October.

Step 3: Pruning

If required, pruning is best done in late winter or any time before August 1. For best practices on how to dispose of clippings or if removal of the plant is necessary, please follow the guidelines at LandscapeOntario.com/box-tree-moth-disposal to help prevent the spread of this pest to locations where it is not present.