grey grubs in the lawn

(Question)

We live in Toronto. Sunny, dry conditions, clay soil with about 4 inches topsoil.

How do we control grey grubs in the lawn.

(Answer)

Your question is very timely!

Grubs are the larval form of a variety of insects, most commonly Japanese Beetles, June Beetles and European Chafers. When the grubs are very young, they can’t eat much so the damage to the lawn in minimal; but by late summer, they are full grown and devouring the grass roots. In addition, they are joined by grubs that overwintered deep in the soil last year and have migrated to the earth nearest the surface of the soil by this time. I expect that’s why you have started to see damage, such as patches of dead grass that lift up easily because the roots are almost gone. In addition, skunks, moles and raccoons may be digging up your lawn to feed on the grubs.

On the Ontario Ministry Agriculture, Food and Rural Affairs website you can see photos of various types of grubs.

August is a good month to control the grub population. We don’t recommend Japanese beetle traps, since it is possible that they will simply attract more beetles to your lawn, where they will lay more eggs, adding to the grub population.

We suggest using beneficial nematodes, which are tiny roundworms that you can purchase at most garden centres. Watered into the soil, they immediately begin infecting the grubs. They release bacteria into the grubs, which kills them after a few days. Since the nematodes can only feed on their bacteria, they cannot harm people, plants, or animals.

You will not destroy the entire grub population in this fashion, but a healthy lawn can generally exist with 3-5 grubs per square foot. At that volume, the grass should be able to regrow roots at a rate that keeps up with the grubs.

You may decide that you would prefer to replace your lawn with an easier-to-care-for, more environmentally friendly alternative. To explore that idea, take a look at our Gardening Guide on Lawn Alternatives and Organic Care of Groundcovers.