Grubs can cause havoc on a lawn, usually during the spring and fall months. To test whether grubs are in fact the culprits of your damaged and yellowed lawn, cut a grass square that is about 12 inches long on each side and about 2 inches deep. Look under the patch of grass to notice any grubs. If more than 50 percent of the area is covered with grubs, your lawn is heavily infested. In Montreal, you most likely have white grubs, which are larvae from June and Japanese beetles.
Collect the grubs above ground in the early morning around dawn. Grubs are not in their active stage at this time and can be picked up by hand. Discard the grubs in a bucket of soapy water. You can also use a vacuum to suck them up. Discard the bag after each use.
Trap grubs by hanging up a white sheet with a light behind it. Under the sheet, place a bucket of soapy water. In the morning, shake the grubs into the bucket.
Attract birds to your property. For example, install birdhouses or broadcast a handful of birdseed or pieces of bread. The birds will eat your grubs to help control the population and minimize their damage to your grass.
Purchase entomopathogenic nematodes from your local nursery if your lawn is heavily infested with grubs. You will need about a billion per acre of lawn. Entomopathogenic nematodes are parasitic roundworms that will enter the grubs and kill them. It will not harm the plants and animals nearby.
Verify Montreal laws on the use of insecticides if all other measures are ineffective. As of 2010, there are no insecticides permitted that work effectively to kill grubs. However, if one does become approved, such as Bacillus thuringiensis, var. japonensis, which works to kill white grubs, apply it at a rate recommended on the label. The Montreal Botanical Gardens' website has a list of pesticides, including insecticides, that are permitted for home use in Montreal.