White grubs are the larval stage of various scarab beetles, representing one of the most common and destructive lawn pests. These soft-bodied insects spend their lives underground, feeding on the roots of grasses and ornamental plants. While a healthy lawn can tolerate a small number of grubs, a large infestation quickly leads to widespread turf damage. Successful management relies on understanding their appearance and life cycle timing.
Identifying White Grubs and Key Species
White grubs are typically creamy white or grayish-white with a distinct brown or reddish-brown head capsule. They are characterized by their soft, plump bodies and their tendency to curl into a distinctive “C” shape when found in the soil. Grubs possess three pairs of short legs near the head, and their size can vary from about 3/8 inch to nearly 2 inches long, depending on their age and species. The darker area at the tail end is simply soil and digested matter showing through the skin, a common identifying feature.
These larvae belong to the Scarabaeidae family of beetles, and several species cause turf damage. The most frequently encountered pest species include the grubs of the Japanese beetle, the European chafer, and the May/June beetle. While all white grubs look similar, their exact species can sometimes be differentiated by the specific pattern of hairs on the last segment of their abdomen. The May/June beetle larva is larger and has a life cycle that can span multiple years, unlike the one-year cycle of the Japanese beetle or European chafer.
Understanding the Grub Life Cycle
White grubs undergo complete metamorphosis, which involves four distinct stages: egg, larva, pupa, and adult beetle. Adult beetles typically emerge from the soil in early to mid-summer, with species like the European chafer emerging in June and the Japanese beetle in July. The females then lay their eggs in the soil, often preferring moist, healthy turf, and these eggs hatch within a couple of weeks.
The larval stage is when the insect causes damage by feeding on grass roots just below the soil surface. The newly hatched grubs, known as first-instar larvae, are small and begin feeding immediately, but the most aggressive and damaging feeding occurs in late summer and early fall. As temperatures cool in the late fall, the grubs move deeper into the soil to overwinter, becoming dormant.
In the spring, the grubs move back toward the surface for a brief period of feeding before they transform into the pupal stage, typically around late May. This spring feeding period usually causes less severe damage than the fall period because the grubs are preparing to pupate, not actively growing. The timing of treatment is directly linked to this life cycle; the grubs are easiest to target when they are small and close to the surface, which is usually from late July through September.
Recognizing Signs of Lawn Damage
The damage caused by white grubs often appears as irregular patches of grass that begin to wilt, thin, and turn yellow or brown, even when the lawn receives adequate water. This discoloration is a direct result of the grubs severing the grass roots, which prevents the turf from absorbing water and nutrients. An infested area may also feel unusually soft or “spongy” underfoot because the root structure holding the soil together has been compromised.
In cases of heavy infestation, the turf can be easily lifted or rolled back like a piece of carpet, revealing the grubs feeding just beneath the surface. To confirm a grub problem, homeowners can cut and peel back a square foot section of sod in a damaged area. Finding ten or more grubs in that single square foot sample is generally considered an infestation level that warrants a control measure.
Secondary damage caused by predators is another frequent sign of a grub problem. Animals like skunks, raccoons, and birds are attracted to the high-protein food source and tear up the turf while digging for the grubs. This digging activity, especially in late summer or early fall, often provides the first visible warning that a large population of larvae is present.
Management and Treatment Options
Effective management relies on selecting the correct treatment type and applying it at the most vulnerable stage of the life cycle. Chemical control is divided into two primary strategies: preventative and curative treatments.
Preventative treatments, such as products containing imidacloprid or chlorantraniliprole, are applied earlier in the season, typically from mid-June to mid-July. These systemic products are absorbed by the grass roots and remain in the soil to kill newly hatched grubs before they cause significant damage.
Curative treatments, which often contain trichlorfon, are applied later in the summer, usually from mid-August through September, after damage is noticed. These products are faster-acting and designed to kill larger, actively feeding grubs on contact, but they have a shorter residual effect than preventative options. For both chemical types, approximately a half-inch of water must be applied immediately after application to move the insecticide down into the root zone.
Beyond chemical options, biological controls and cultural practices offer alternative management methods. Maintaining a healthy, well-irrigated lawn helps the grass tolerate some root loss without showing signs of stress. Beneficial nematodes (Heterorhabditis bacteriophora) are microscopic organisms that seek out and kill grubs, and they are most effective when applied to small, young grubs in warm, moist soil. The bacterium Paenibacillus popilliae, known commercially as Milky Spore, has historically been used, although research suggests its effectiveness can be limited and highly variable.