Grub worms are the destructive larvae of various beetles, such as Japanese beetles and June bugs. They live just below the soil surface, feeding voraciously on grass roots. Left unchecked, a severe grub infestation can destroy a healthy lawn in a matter of weeks.
Identifying Grub Damage
Grub damage typically appears in late summer or early fall as irregular patches of dying, yellow, or brown grass. Because the roots have been severed, you can literally roll the dead turf back like a piece of carpet. If the grass lifts easily, suspect grubs.
Secondary Signs of Infestation
Often, the first sign of grubs isn't the dying grass, but the animals hunting them. Raccoons, skunks, and crows will tear up your lawn searching for these protein-rich snacks. If your lawn looks like it was dug up overnight, grubs are likely the cause.
How to Check for Grubs
To confirm an infestation, cut a one-foot square section of turf at the edge of a dying patch and peel it back. Count the white, C-shaped grubs in the soil. Finding 1 to 5 grubs is normal, but 10 or more per square foot requires immediate treatment.
Curative vs. Preventative Treatments
If you have an active infestation causing damage, you need a curative insecticide containing trichlorfon or carbaryl, which kills grubs on contact. Preventative treatments, containing imidacloprid or chlorantraniliprole, should be applied in early summer before eggs hatch.
Repairing the Damage
Once the grubs are dead, you must repair the rootless turf. Rake away the dead grass, aerate the compacted soil, and overseed the bare patches. Keeping the lawn well-watered will help surviving grass regenerate its root system before winter.