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How to Treat Boxwood Moth

Boxwoods are a popular plant in Toronto and GTA gardens, but this species can be susceptible to pests like boxwood moth.

Torontonians appreciate boxwoods for their tidy look, tolerance for pruning, and ability to grow as a hedge or privacy barrier. They’re also a low-maintenance plant.

Popular species include the green gem boxwood and winter gem boxwood. However, this shrub has a number of enemies in southern Ontario, including wind and sun damage, leaf miner, fungus and boxwood moth.

Boxwood moth, also known as box tree moth, is a relatively new threat in Ontario. This moth feasts on your boxwood plants, damaging leaves and stems. To add insult to injury, boxwood moth has made an early appearance in 2021.

What is Boxwood Moth?

Boxwood plant closeupThe box tree moth is native to eastern Asia and was first noticed in Toronto in 2018. It’s also known as an invasive species in Europe. It’s part of the Crambidae moth family. This moth makes its home in all species of boxwood.

So far, they have been found in a relatively limited area closer to Lake Ontario. This area extends from Etobicoke to the Scarborough Bluffs.

How to Identify Boxwood Caterpillar and Moth

White coccoons on your boxwood leaves are the most obvious early sign of box tree moth. You may also see leaves stuck together by the cocoon. They can be found from early spring. Inside the cocoon, you’ll find green larva. If there are eggs in the cocoon, it’s a spider nest, not a moth. Once the larva grow into green caterpillars, they are easy to identify.

Around mid-May, the larvae begin to hatch. After this, you might see signs of the moth eating away your boxwood plants. When young boxwood caterpillars feed on the leaves, the leaves eventually dry out and turn brown. Mature caterpillars will eat the leaves entirely, leaving only the ribs.

Biologists believe the GTA sees two generations of boxwood moth over the summer.

Why Are Boxwoods Vulnerable?

Boxwood plant with ice in winterAs an imported species, boxwoods are vulnerable to a number of diseases and pests. The box tree moth is one of these. Boxwood blight, boxwood leaf miner and boxwood mite are also common. Boxwood trees also see “winter bronzing,” where leaves become yellowish or reddish-brown from wind and sun exposure. Proper watering during the growning season helps prevent this.

Fungal issues, leaf spot, and root rot (where drainage is poor) are also common boxwood problems. New growth can also be damaged from cold winter weather.

Boxwood Moth Treatment Options

How do you get rid of boxwood moth? This pest needs to be treated with an insecticide. In Ontario, that means you’ll need a licensed arborist or other pest management professional to treat your boxwoods. The boxwood moth can be managed through a safe biological insecticide that’s also used to treat gypsy moth infestations.

An arborist can also prune off heavily infected portions of your boxwood to preserve the rest of the plant. Any removed plants or branches need to be disposed of safely. The City of Toronto recommends that infected plants be left outside in a black plastic garbage bag for several days, then disposed in the garbage (not your yard waste).

Repeated spraying throughout the summer season can be necessary for pervasive infections. The second generation of boxwood moth usually appears around the middle of the summer, making this a good time for a second spraying. They may also appear in early September.

Ready to keep your boxwood plants safe from the box tree moth? Give us a call for pruning, boxwood moth spraying and infestation control.

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