If your grass turns brown and pulls up easily in July and August, or if you notice a lot of critters such as skunks or raccoons tearing up your lawn, your grass may be infested with grubs. White grubs are the larvae of Japanese beetles, June beetles, or masked chafer beetles. They cause damage to lawns by feeding on the roots of grass.
Identifying the Pest
Grubs are milky white with a brownish head. They typically curl into a "C" shape when disturbed. Depending on species they may have a 1-year or a 3-year life cycle. Annual white grubs (larvae of masked chafer beetles or Japanese beetles) begin their life cycle in mid- to late summer, grow quickly, and do most of their feeding in late summer. Larvae of June beetles take 3 years to complete their life cycle, so damage from them may appear in lawns in spring, summer, or fall.
When to Control Grubs
Controls are most effective on immature grubs. For most species and locations that means July or August is the prime time to treat with an insecticide. However, because grub populations vary from year to year, you may be able to save the cost of treatment if you first sample your lawn to estimate how many grubs are present. Dig up several pieces of sod about a foot square. If you find five or fewer grubs per square foot, you need not apply grub control. The lawn will withstand the amount of feeding these few grubs do. If 10 or more grubs are present, treat your lawn for grubs. If the average count is between five and 10, whether or not to control depends on the health of your lawn, your tolerance for damage to the lawn, and presence of natural controls.