Lawn grubs, often called white grubs, are the immature form of different scarab beetles, such as Japanese beetles, June “bugs” (beetles) or the European chafers. These white, C-shaped creatures have soft bodies with legs near the head. They feed on grass roots (and organic matter in the soil), causing sections of grass in the lawn to die. Grubs eventually turn into adult beetles and emerge from soil to mate and lay eggs, which hatch into more grubs.
Most scarab beetles have a one-year life cycle; June beetles have a three-year cycle. Timing varies by beetle species and region, but generally adults emerge from soil, mate, and lay eggs over the course of two to three weeks in early to midsummer.
Depending on soil moisture and temperature, eggs hatch about two weeks after being laid, in mid- to late summer. The new generation of root-munching grubs begins feasting immediately after hatching.
Peak grub feeding occurs in early fall. Typically grubs operate a few inches below the soil surface, but burrow deeper (up to 8 inches in northernmost areas) before winter arrives.
Inspect your lawn to confirm grubs are present, and determine the extent of the infestation. A healthy lawn can easily support a grub population of zero to five grubs –and possibly as many as nine per square foot.
Scout a lawn in late summer by digging several sections of sod 1 foot square and 2 to 4 inches deep. If grubs are present and feeding, you’ll see them in soil. Follow these treatment guidelines:
While turf is lifted, grab any grubs you see and toss them into a can of sudsy water. Water turf after replacing it.
Immature grubs are most susceptible to pesticides while young. For most white grubs this means applying pesticides while newly hatched grubs are feeding – in mid- to late summer and early fall.
A curative product kills existing grubs on contact. A preventative pesticide kills grubs over a longer period of time – those that are present at the time of treatment, as well as those that hatch during the season of application. Because the preventative contains nitrogen fertilizer, it’s important to keep lawns irrigated after application to avoid burning grass in summer heat.