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These 3 pests with rising populations can decimate Vancouver Island foliage

The spongy moth is dangerous as ever despite government intervention

The spongy moth is back and dangerous as ever, says one Vancouver Island arborist.

Formerly known as the gypsy moth, the Lymantria dispar moth was introduced from Europe to the northeastern U.S. in 1869. The North American strain of the moth was first seen in B.C. in 1978. They’re a massive problem in Ontario, and trying to become one here in B.C.

The damaging part of their life cycle is the larval stage, as caterpillars will completely defoliate a tree, Dan Sharp told Black Press Media.

“Trees are resilient, they’re strong and adaptive but it does drain on their nutrients,” said Sharp, district manager for Davey Tree in Victoria.

The tree must dip into its energy resources, and if that happens year after year it creates a stressed tree, which becomes a target for other pathogens and insects. The tree likely won’t have the strength to fend off those attacks.

The spongy moth has been around a long time, residents should be familiar with the provincial response and bid to eradicate it using aerial sprays.

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This spring the Ministry of Forests sprayed 50 hectares in View Royal, 402 hectares in Lake Cowichan and more than 1,068 hectares in the Nanoose/Lantzville/Nanaimo area with insecticide to combat the invasive spongy moth, citing its danger to food crops including apples and blueberries, and trees including Garry oak, arbutus, red alder, aspen, cottonwood, maple, orchard fruit trees and nut trees.

Their population in the sprayed areas has increased drastically according to 2021 trapping and monitoring data from the province. Egg clusters are typically transported to B.C. on clothes and recreational vehicles from outside the province.

Spraying on Vancouver Island wrapped on June 21, and the next stage in the ongoing process is to monitor and assess trapping results over the summer and by late fall, determine if this year’s efforts were successful and if treatments will be required in 2023.

If it becomes too established it will be impossible to control, much like Ontario’s struggles, Sharp said.

Now is a good time to monitor and report.

“The timing for treatment on the caterpillars is first thing in the spring,” he said. That’s because they’re microscopic when born and will have heavily damaged a tree by the time they’re visible. He recommends watching for holes and to report to the province and local arborist if they’re spotted.

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Residents should also watch for two other insect populations on the rise – the winter moth and the bronze birch borer.

The winter moth has a different life cycle and emerge as moths in late fall, which puts them in the defoliation caterpillar phase in early spring.

The bronze birch borer is a native beetle, but overly abundant. Much as the name implies, it’s a brown bug that digs into birch flesh. When you see a birch dying from the top down it’s generally courtesy of the beetle, Sharp said.

While it is native, the bug feeds preferentially on the introduced white birch in the region – popular with homeowners and for streetscapes. Because it digs in, there are few remedies at the moment.

Sharp says they’re working on attaining approval for an injectable pesticide, with trials underway for new products to control them in a bid to keep urban trees healthy. They hope to see results in the next year or two. In the meantime, arborists can only prune out the damage, fertilize and mulch to keep the tree healthy and hopefully thriving.

Christine van Reeuwyk

About the Author: Christine van Reeuwyk

Longtime journalist with the Greater Victoria news team.
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