In the late summer of 2018, box tree moth adults were detected in Etobicoke, Ontario. Since the initial detection, active populations have been identified within the following area; South of Steeles Ave, west of Leslie Rd and east, north of the Gardiner Expressway, and east of Highway 427. Fortunately, there have been no observations of this pest outside the specified area.

The box tree moth is native to eastern Asia (Japan, China, Taiwan, Korea, the Russian Far East and India). All species and cultivars of Buxus are believed to be hosts for box tree moth. It is possible that the moth may feed on Japanese spurge (Pachysandra terminalis), although the insect prefers to feed on Buxus spp.

Box tree moth caterpillars begin feeding in early May once the temperature reaches approximately 15 C. After about 14 days of feeding, the caterpillars reach maturity and begin to pupate. Adult moths emerge about two weeks later, mate, and lay eggs. There are believed to be 2 generations in Toronto per year.

What to look for: 

Examine all boxwood plants for signs of chewed leaves, larvae, webbing and frass (bodily excretions). Larvae feed from May to September

Little white sacs between leaves: Box tree moth larva overwinters inside a hibernarium until the warm days of May.

Box tree moth hibernarium image

Young caterpillar feeding: Young box tree moth caterpillars feed on surface tissue of the leaves. Eventually these leaves will dry out and turn light brown in colour.

box tree moth early feeding image

Mature caterpillar feeding: Mature caterpillars have larger mouthparts and will consume large portions of the leaves, often leaving only the midribs, and occasionally the outer margin intact.

box tree moth late feeding image

Webbing and frass: One of the most obvious signs of an infestation is the webbing produced by the caterpillars as they feed. The caterpillars and their frass can often be found inside the webbed leaves. Caterpillars can range in size from 4mm to 4cm long, depending on their stage of development.

box tree moth webbing and frass

What you can do:

Since box tree moth is a garden pest and only infests boxwood species, it is not considered a forest health concern; Therefore the City of Toronto does not treat for box tree moth. While box tree moth can pose a serious threat to boxwood species, if caught early, the effective use of biological pesticides has proven to be successful in managing this pest.

  • Box tree moth caterpillars can be effectively managed with Dipel, a biological insecticide containing a naturally occurring bacterium, Bacillus thuringiensis (B.t.), which causes the caterpillars to become ill after feeding on sprayed foliage. Within hours of ingesting the B.t. residue, the caterpillars stop feeding and will eventually die after 2-3 days. 
  • The active ingredient of the spray is safe to humans and pets and is the same as the one in BTK caterpillar killer.
  • B.t. based products can be found at most retail garden centres or can be applied by a can be applied by a licensed spray contractor.  

When pruning or disposing of infested boxwood shrubs, place plant material in a black plastic bag and tie it off securely. Allow the bag to sit in the sun for a minimum of two days to kill any box tree moths inside. Ensuring the moths are dead will prevent the further spread of the insect.

Reporting:

This pest is being monitored closely by Landscape Ontario and the Canadian Food Inspection Agency. If you wish to confirm the presence of box tree moth and/or require any further information regarding treatment options, please refer to the following website

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