A handful of trees along Granite Street feature a swatch of what looks like cling wrap wrapped around their trunks, a few feet from the ground.
They’re Garry oaks banded to stop winter moths climbing the trunk to lay eggs. When those eggs hatch in spring, they turn into small green worms or loopers that eat the tree’s leaves.
“We monitor populations and treat susceptible trees with tanglefoot or sticky bands if we reach a certain threshold that could lead to tree mortality. We rarely see this threshold as there is a parasitic fly that keeps populations in check and most trees will tolerate a certain level of winter moth infestations very well,” parks manager Chris Hyde-Lay explained.
Most Oak Bay winter moth banding efforts focus on susceptible young or newly planted trees because spring defoliation can set a tree back during its establishment period. It can even kill individual defoliated branches or, in the worst case, an entire tree.
Staff also periodically band larger trees like Garry oak and birch that seem to have a more genetic susceptibility to winter moth attack.
The spring hatch also fills the air with dangling green worms that drop on unwary pedestrians, but the larger concern, Hyde-Lay said, is protecting residents’ fruit trees.
“Once inside, the buds the winter moth caterpillars feed and destroy the flower parts, hence reducing the fruit crop considerably. A homeowner really has to be vigilant and keep an eye out when the fruit tree leaves are just breaking in spring and look for the winter moth as they roll themselves up in the leaves,” Hyde-Lay said.
By then it’s too late to band the tree as the female has already crawled up the trunk and into the crown to lay her eggs. Then he recommends controlling the outbreak using organic insecticide treatments.
There are two other defoliating predator pests high on the parks staff least wanted list – the linden looper that loves to munch on Garry oak and satin moth, guilty of defoliating aspen trees in Uplands Park.
Fortunately, the linden looper population is in decline thanks to natural control through parasites and disease.
The satin moth is a more pressing concern, as the Oak Bay aspen grove they routinely defoliate near the cenotaph is part of a red listed plant community. The satin moth produce two rounds of leaf-eating caterpillars in a season, stripping a tree twice a year.
Mature healthy trees normally have enough resources stored to recover, but repeated, severe defoliation over many seasons can result in tree death, Hyde-Lay said.
The population was down slightly but remained high last year.
“We are hoping that this year the several parasitoids and predators that keep this insect in check will increase in population,” he said.
Staff plan to watch both pest populations closely.
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