Spraying put on hold in gypsy moth fight against invasive pest
More monitoring and sticky bands may be better egg options
The Hamilton Conservation Authority will expand its monitoring of gypsy moth eggs in Ancaster and at Iroquoia Heights this winter before assessing the need for an aerial spraying of a biological pesticide to combat the invasive pest.
Terrestrial ecologist Lesley McDonell said this spring’s infestation in the Dundas Valley went mostly as expected in areas surveyed last winter with moderate defoliation of trees by the Hermitage in Ancaster.
But she said a more severe defoliation that was expected in a stand of walnut trees south of Little John Road by University Plaza in Dundas turned out to be moderate.
McDonell said assessing the damage from the gypsy moth caterpillars was complicated by an outbreak of fall cankerworms, which also devoured tree leaves this spring.
She said this winter’s monitoring will be expanded to locations by Jerseyville Road and additional areas by the Hermitage where gypsy moths were the confirmed culprit, as well as at Iroquoia Heights.
“It’s usually about an eight-to-10year cycle, so it seems be on the rise now, and unfortunately it kind of coincided right with the fall cankerworm,” McDonell said.
“The fall cankerworm we’re not as worried about because it is a native pest and our birds and chipmunks and squirrels, they like to eat those caterpillars, same as gypsy moths.
“But they tend to bring down that population quickly.”
McDonell said the authority is discussing the possibility of an aerial spraying next spring with the city and other municipal partners but will monitor egg populations in the meantime.
She recommended against spraying this year because, apart from being expensive, the favoured Btk biological pesticide kills other moths and butterflies at the same development stage.
McDonell said some less costly measures proved effective, including placing sticky bands around the trunks of heavily infested trees by Little John Road to catch the moths in their caterpillar stage.
“We have trees, side by side — one that was sticky banded and one that wasn’t — and the one that wasn’t is completely defoliated at the top and the one that had the sticky band still has about 50 per cent of its canopy,” she said.
McDonell said this year’s wet spring and summer may also be helping combat the infestation in two ways.
Trees are better able to re-grow leaves after defoliation, and the wet conditions are good for a fungal virus that kills the caterpillars naturally, she said.
“We’ll only see that when we actually do our surveys again. If we find dead caterpillars or if we see less egg-mass production, then that means some of caterpillars were killed by this virus.”