Boxwoods are planted as ornamentals and typically used for edging, as hedges, and/or clipped into different shapes to make topiaries (Figure 1). However when infested, the plants are disfigured by the loss of leaves, by webbing spun by the larvae, as well as larval excrements (Figure 2). Larvae feed principally on leaves of the host but may also attack the bark.
Box tree moth was detected in Toronto in August 2018 by a citizen scientist as reported in an online publication (see iNaturalist.org's Blog). In November 2018, the Canadian Food Inspection Agency (CFIA) confirmed the presence of box tree moth in an urban neighbourhood in Toronto. This is the first confirmed report of this pest in North America.
Detection and identification
Damage to boxwood plants is caused by the larvae feeding primarily on leaves and sometimes on the bark. Infested plants are disfigured by the loss of leaves and by the webbing spun by the larvae. Younger larvae feed by eating the lower surfaces of the leaves only, leaving the upper epidermis intact. Older larvae feed inside the webbing and skeletonize the leaves, leaving only the midribs, and occasionally the outer margin intact. Presence of webbing, frass (excrement), and moulted black head capsules may also be apparent in and around infested plants. The defoliation and dieback are unsightly, and reduce the value of the plants.
Prevention and control
At this time, raising public awareness on the risk of moving infested boxwood material is essential to help control and limit the spread of C. perspectalis in Canada. Boxwood plants can be infested with all life stages of the box tree moth. In Europe, chemical treatments and biopesticides are available for use on boxwood; however many of these compounds may not currently be registered for use on boxwood or available in Canada. Shady Lane Expert Tree Care will be using B.t. (Bacillus thuringiensis) to control Box Tree Moth larvae.
To help determine the extent of its distribution, the CFIA is encouraging all stakeholders to submit samples of any pests they observe on boxwood plants to their local CFIA office. Suspect sightings can also be reported online. This information will assist in evaluating the threat and will help direct the next steps for Canada.