By Yen Yen Yip
Something is bugging many Ottawa gardeners this year.
White grubs are having a field day feeding on grass roots, and lawns that used to be lush green are coming apart in brown tufts.
“The roots completely disappear, (and the lawn) just becomes a little mushy patch that you can scrap off with a rake,” says Nicholas Bott, owner of the Lawn Clinic, a grass maintenance company.
Although the grub-infestation problem is more rampant in Ottawa’s west-end, Bott has received about 50 calls from lawn-owners in the Centretown area who’re trying to ward off the creepy-crawlies in order to protect their lawns.
That’s a huge jump in numbers compared to last summer, he says, when grubs posed virtually no problem.
The prevalence of the grubs is partly due to their two-year life cycles – and this year happens to be peak season for hatching larvae. Adult bugs typically lay their eggs in June, when soil temperatures get warmer. The eggs hatch into larvae, which mature and become adults after their first winter.
In between summer and winter, the white grubs burrow underground and eat, and eat, and eat. The effects of their feeding become noticeable around this time.
A dry summer has compounded the problem.
“When grass is in water, it can heal itself fairly quickly as it’s being attacked,” says Bott. But grass stops growing and depends on root reserves in dry weather – which is why it dies so easily and peels like a carpet when grubs destroy the roots.
Bruce Gill, an entomologist at Agriculture Canada, says the introduction of a new insect is another factor. Since the European chafer beetle moved in with chinch bugs, June beetles, crane flies and other members of Ottawa’s native bug family about 10 years ago, larvae populations have been increasing.
“The European chafer beetle is often an urban problem, because it’s moved in sod when people re-do their lawns,” says Gill.
He also notes that white grubs usually hit population highs after 10 to 20 life cycles – and that although larvae growth might be nearing its peak this year, it could continue to climb.
But he stresses the outbreak in white grubs isn’t anything to get agitated about.
“You get sort of good years for the grubs, which would be a bad year for people trying to grow lawns,” he says. “Most of them are natural population fluctuations … they go up and down.”
But that’s why chemicals to control the bug problem, such as diazinon, have been selling like hot cakes.
“We’ve felt the pinch with keeping the product in stock,” says Bob Shane, a manager at The Weedman, a lawn care business where sales of diazinon have increased at least a hundred-fold in treating grub-infested lawns this summer.
Diazinon is biodegradable and won’t harm birds and mammals if label rates aren’t exceeded.
The pesticide run-off, however, can attack other insects in the garden, according to Gill. If predator bugs that act as natural controls for some insects are killed, that can lead to problems with other pests later on.
He says that microscopic parasitic organisms called nematodes that kill larvae but are harmless to critters like earthworms, can also help if applied early in the season.
City officials say they haven’t noticed any grub problem in Centretown parks.
But if the grass is infected, adds Ray Yantha, Ottawa’s manager of parks and trees, the only option would be re-sodding next year – the city banned the spraying of chemicals.