Your best defence against grubs – any pests for that matter – is a healthy, properly fed lawn. Simply because you have grubs in your lawn or garden does not mean treatment is necessary. Grubs – like most insects – actually benefit soil structure. They also help keep the soil aerated much like earthworms do. However, when populations of grubs reach a certain point your lawn’s health can be effected. Research shows that a healthy lawn can have as many as 10 grubs per square foot without harming it. If your lawn is developing irregular-shaped brown patches it may be time to investigate. Try to pick up the green sod “by the hair” and peel if back at the edge of the brown patches. If it peels back easily and exposes grubs (mushy, creamy-white “c-shaped worms”) your lawn has likely reached the point where treatment is necessary to prevent further damage.
Beneficial nematodes – microscopic parasitic worms available at most garden centres – are the only treatment available at this point in Ontario. Proper timing is critical, however. It is also important to water them into the soil thoroughly for maximum effectiveness. The key word is these little guys need to “swim” to their hosts (grubs). Soil must be kept moist for ten days minimum to allow them to mature properly while they do their “damage”. It has been my experience that spring nematode applications do not work. Early to mid August is probably the earliest for effective control. This is also a good time to re-seed the damaged areas. Grubs will not harm seed as it comes up. It is pointless to treat for grubs at the wrong time. If your lawn has a history of severe grub infestations it may be necessary to hire a professional for both advice and a properly-timed preventative treatment.