August 9, 2021
Box Tree Moth is an invasive pest that causes severe damage to boxwood.
Box Tree Moth is an invasive pest that causes severe damage to boxwood.

Scouting box tree moth

We have come to a time in the progression of the Box Tree Moth situation where it is now important for Canadian nursery growers, especially those in Ontario, to closely monitor their boxwood, incoming boxwood and their facility for any signs of the larvae or moth. Late in April, moths were trapped in a propagation greenhouse in Niagara, which is the first-time Box Tree Moth has been detected on a farm setting in Canada. This was a surprise to us all, as last year’s trapping did not indicate the presence of the moth outside of the Toronto core zone.

Box Tree Moth overwinters as an early instar larva, wrapping itself in webbing between two leaves. This is referred to as a hibernarium. Larvae emerge in late April or early May, depending on the temperatures, and begin feeding on boxwood leaves. They also leave webbing on the leaves, which is one of the most obvious signs of infestation. Since the small mouth parts of the larvae only remove the epidermal layer of the leaf, early instar feeding damage results in a characteristic windowpane effect. Later instars can eat the entire leaf, but leave the leaf margin behind, again another characteristic feeding sign of BTM larvae.

Following pupation, the moth emerges and can fly up to 10 km from the site of its emergence. Eggs are laid by the moth on the underside of boxwood leaves, usually in a cluster of about 10 to 20 eggs and are very difficult to detect. The eggs hatch after about three days and the second generation begins. This second, or summer generation, is not as synchronous as the spring one, with overlapping larvae and pupae stages.

What this means though is there are two generations of adult moths per year. It is recommended that pheromone traps be placed around the perimeter of the host plant production area at a density of four traps per hectare or spaced no less than one every 100 metres. The traps should be hung from June 1 to September 30 and checked weekly. If you have a greenhouse used to propagate boxwood, place a trap inside the greenhouse as soon as mid-April.

Box Tree Moth is not a regulated pest in Canada, but it is regulated in the United States. However, it is a pest of concern, which does require that a farm notify CFIA if they do detect any life stages of Box Tree Moth at their facility. Currently, there are no regulations for domestic movement of boxwood. The United States has imposed import requirements that include not just boxwood, but euonymus and ilex species too. To export these to the United States, CFIA must issue an additional declaration on the phytosanitary certificate prior to shipping. If exporting, please take extra precautions to ensure the boxwood you are shipping is free of any signs of larvae or feeding damage. If this pest is found at a border inspection, the ramifications for future exports, although unknown, could be very significant.

The Landscape Ontario Box Tree Moth Industry Working Group and the CFIA Technical Advisory Committee have been very active on this file since early 2019. As a result, there are many resources out there available for your use. To review these materials, it is highly recommended that you search Box Tree Moth on as well as on, an excellent blog from OMAFRA’s Nursery Specialist, Jen Llewellyn.

CNLA has also been working on the development of a Box Tree Moth module for the Clean Plants program. The best management practices for the module are essentially complete.

If you would like to receive a copy of these BMPS to help develop systems for your farm to monitor for Box Tree Moth, or if you have any questions on this pest, please contact: