Lawn grubs in Ontario are controlled naturally through lawn care that helps turf tolerate feeding, beneficial nematodes applied in late summer while grubs are small, and keeping skunks and raccoons from tearing up the turf to eat them. Knowing which grub species is present matters, since nematodes work much better on some species than others, and the province's cosmetic pesticide ban rules out most chemical grub treatments on home lawns.
What Causes Grub Damage in a Lawn?
White grubs, the C shaped larvae of several beetle species, feed on grass roots just below the surface, cutting the turf off from the water and nutrients the roots supply. Early damage looks like drought stress, with patches that wilt and turn brown, and badly damaged turf lifts away from the soil like loose carpet.
Much of the visible destruction comes from animals hunting the grubs. Skunks and raccoons pull back the turf to feed on grubs in spring and fall, and flocks of starlings, blackbirds, or crows working one patch of lawn are another common sign that grubs are present.
Which Grubs Are Eating an Ontario Lawn?
Three species of white grub damage Ontario lawns: the European chafer, the most common, plus the Japanese beetle and the June beetle. Full grown grubs range from about 2 cm for a Japanese beetle to 4 cm for a June beetle, and the European chafer and Japanese beetle complete their life cycle in one year, while the June beetle takes three.
The species can be told apart by the pattern of spines on the underside of the grub's rear end. On a June beetle grub the two rows of spines run parallel and meet at both ends, on a European chafer grub they run parallel and then spread apart at the tip, and on a Japanese beetle grub they form a V shape.
How Many Grubs Does a Lawn Need Before Treatment Makes Sense?
Treatment generally makes sense once a lawn holds roughly 5 to 10 grubs per 0.1 square metre, about one square foot, since dead patches tend to appear above that level. Folding back a small square of turf in a few spots and counting the grubs underneath gives the number, and mid August is a good time to check, once that year's eggs have hatched.
Do Beneficial Nematodes Work on Ontario Grubs?
Beneficial nematodes, microscopic roundworms that enter a grub and kill it, are one of the main biological options left to Ontario homeowners since the cosmetic pesticide ban took effect in 2009. The species most often sold for grubs, Heterorhabditis bacteriophora, gives good control of Japanese beetle grubs but is less effective against the European chafer, so checking the species first avoids paying for a treatment that underperforms.
Timing matters as much as species. Treatment works best just after the young grubs hatch, from mid to late August into mid September, applied in early morning or late in the day to avoid heat and sunlight, watered in immediately, and kept moist for one to two weeks afterward. Nematodes are a living product, so they need careful storage and should be used soon after purchase.
Which Lawn Care Habits Make Grub Damage Less Likely?
A thick lawn mowed at 6 to 8 cm grows deeper roots that can tolerate some grub feeding without dying back. Watering deeply about once a week, rather than lightly every day, keeps turf healthy, and lawns with enough rainfall or regular irrigation generally show less grub damage.
The exception is midsummer, when adult beetles are laying eggs. Watering heavily during peak beetle activity, especially when surrounding yards are dry, draws egg laying females to the one green lawn on the street and helps their eggs and young grubs survive.
How Can Skunks and Raccoons Be Kept From Tearing Up the Lawn?
Controlling the grubs removes the reason animals dig, but turf can be torn apart overnight while a treatment is still taking effect. Urban Nature Store's guide to keeping raccoons out of a yard lists torn up lawn and fresh sod as one of the signs raccoons are searching for grubs.
A motion sensor that fires a short burst of water at anything within about 36 feet is the core of the Hydro Critter Blaster, a solar powered sprinkler whose maker lists both raccoons and skunks among the animals it repels. Pointing it across the damaged section protects up to 1,200 square feet of lawn without chemicals while the grub population comes down.
Frequently Asked Questions
Can grubs be treated in spring instead of late summer?
Less effectively. Spring grubs are larger and close to the end of their feeding, so late summer, just after the new generation hatches, remains the better window for treatment.
Do birds pecking at a lawn mean there are grubs?
Often. Flocks of starlings, blackbirds, or crows feeding in the same patch of turf are a common sign of grubs, and folding back the turf in that spot confirms it.
How can a lawn damaged by grubs be repaired?
By overseeding in spring. Once most grub feeding has finished, a top dressing of sand and manure followed by grass seed fills bare patches, and routine mowing can resume once the seedlings are established.
Does fertilizing help a lawn handle grubs?
Yes, with the right balance. A fertilizer high in potassium with enough nitrogen supports the strong root growth that helps turf tolerate grub feeding.
