Lawn grubs are a common, destructive pest that feeds beneath the soil surface, targeting the root system of turfgrass. These pests are the larval stage of various scarab beetles, including the Japanese beetle, the European chafer, and the June beetle (or June bug). Their feeding habits compromise the grass’s ability to absorb water and nutrients, leading to visible damage and eventual turf death.
Identifying the Pest
These larvae are typically called white grubs, identifiable by their distinct physical characteristics. When unearthed, a grub usually curls into a distinct C-shape, with a creamy white or grayish body and a darker brown or chestnut-colored head capsule. They have three pairs of legs located near the head, distinguishing them from legless larvae like billbug grubs. The size of the grub varies depending on maturity, ranging from tiny, nearly translucent larvae to mature forms up to one inch long.
The Grub Life Cycle
Most lawn-damaging grubs follow a predictable one-year life cycle, which dictates when control measures are most effective. Adult beetles emerge from the soil in early summer to mate. Females lay batches of eggs one to three inches deep in the soil, usually preferring moist turf. These eggs hatch into small larvae (first instars) within approximately two weeks, typically in mid- to late summer. The grubs begin feeding immediately on grass roots and organic matter, continuing this phase through late summer and early fall. As temperatures drop in late fall, the grubs burrow deeper into the soil to overwinter, often reaching depths of up to eight inches. They return to the root zone for a brief period of feeding in the early spring before they pupate and transform into adult beetles, restarting the cycle.
Recognizing Lawn Damage
Damage from a grub infestation becomes most noticeable during late summer and early fall when the larvae are largest and feeding most aggressively. The characteristic symptom is the appearance of irregular, brown, and dying patches of grass that fail to respond to watering. As the grubs sever the root system, the turf may feel spongy underfoot. In severe cases, the grass can be easily lifted or peeled back from the soil like a carpet. The lack of roots beneath the lifted turf is a clear diagnostic sign of a grub problem.
Another common indicator is secondary damage caused by foraging animals, such as raccoons, skunks, and birds, digging up the lawn in search of the grubs. These predators can cause considerable damage, often tearing up large sections of turf overnight. A simple diagnostic test involves sampling the soil by digging a one-square-foot section of turf to a depth of about four inches. If the sample reveals a population exceeding six to ten grubs per square foot, significant damage is likely, and treatment is warranted.
Effective Control Strategies
Successful grub management relies on proper timing and selecting the correct product, often categorized as preventative or curative treatments. Preventative control is the preferred approach, using long-lasting systemic insecticides containing chlorantraniliprole or imidacloprid. These products are applied in mid-summer (typically June or July) before the eggs hatch. This ensures the chemical is active in the root zone when the young grubs begin feeding. Chlorantraniliprole offers season-long protection and has a low toxicity profile.
Curative control is necessary when an active infestation is discovered in late summer, early fall, or during the brief spring feeding period. These fast-acting products contain active ingredients such as trichlorfon or carbaryl, designed to kill the larger, actively feeding grubs. Curative treatments are less effective than preventative ones, with success rates varying based on application timing and environmental factors. After any chemical application, watering the lawn with at least half an inch of water is necessary to move the material down into the root zone where the grubs reside.
Biological controls offer an alternative to chemical treatments, most notably the application of beneficial nematodes, specifically the species Heterorhabditis bacteriophora. These microscopic worms search out and kill the grubs by introducing lethal bacteria. Cultural practices also contribute to prevention. Maintaining a tall mowing height and avoiding over-irrigation can make the lawn less appealing for adult beetles seeking a place to lay their eggs.