Adult box tree moths have been observed throughout Southern Ontario over the last couple weeks and as their eggs hatch, early instar box tree moth larvae start to feed again on boxwood shrubs. This second period of feeding activity is the start of the second generation and is your next window to manage the pest, especially just after egg hatch when the larvae are still small.

Regardless of if you’ve seen damage this season or not, now is the time to inspect your boxwoods again and look for signs of small box tree moth larvae (caterpillars) and feeding damage to determine if action is needed. Larvae present now will be feeding over the next few weeks which is the perfect time for management.

A recap of management in the landscape

In residential areas and landscapes, products with the active ingredient Bacillus thuringiensis kurstaki can be used and sprayed on boxwood where larvae are present and feeding. This can be done one of two ways, by hiring a licensed plant health professional/landscaping contractor to inspect and spray your boxwood or by purchasing a BTK product at a home or garden center to spray yourself.

If you are spraying boxwood, the timing to spray is when you see the larvae and ideally when they are still small (which would be now). Ensure thorough coverage of all the leaves. The product must be ingested by the caterpillars to work and can take a couple days until caterpillar mortality. Ensure you inspect boxwood again 7-10 days after a BTK application to determine if treatment was successful or if another application is needed.

Management for nurseries

Applications to target the second generation should be starting this week in most areas, informed by scouting and pheromone trap captures. Commercial nurseries have access to BTK products (such as Dipel, Bioprotec Plus, and Xentari) as well as a NEW product under emergency use called Suspend Polyzone (Active ingredient – deltamethrin). Neither of these products are systemic and therefore thorough coverage of the foliage is needed to achieve good control of box tree moth.