White grubs are the larval stage of various scarab beetles and pose a significant threat to the health and appearance of lawns and gardens. These C-shaped, cream-colored larvae live just beneath the soil surface, feeding aggressively on the fine roots of turfgrass and ornamental plants. Their destructive feeding habits cause substantial, visible damage, often leading to the death of large sections of grass. Infestations require immediate attention, as these pests rapidly undermine the integrity of the landscape.
Identifying the Culprit and Its Life Cycle
White grubs are easily recognized by their distinct appearance: a soft, creamy-white body curled into a “C” shape, a prominent brown head capsule, and three pairs of legs near the head. They are the immature stage of many common insects, including the Japanese beetle, the masked chafer, and various May or June beetles. The larval stage is the only part of the life cycle that causes extensive damage to turf.
The life cycle varies, but many damaging grubs, such as the Japanese beetle and masked chafer, complete their development in a single year. Adult beetles emerge in early to mid-summer, mate, and lay eggs in the soil, often preferring moist, healthy turf. These eggs hatch in late summer, typically late July through August, producing tiny first-stage larvae.
The newly hatched grubs begin their intensive feeding period throughout the late summer and fall, growing larger. As temperatures drop in late autumn, the mature grubs migrate deeper into the soil to survive the winter. They return to the root zone in early spring for feeding before pupating and transforming into adult beetles. Treatment timing is most effective in late summer and early fall when the grubs are young and close to the surface.
Recognizing the Signs of Grub Damage
The most common symptom of a white grub infestation is irregular, brown patches of turf that resemble drought stress. Unlike grass suffering from a lack of water, these areas will not green up after irrigation. The damage becomes most obvious in late summer and early fall when the grubs are rapidly growing and consuming root material.
A definitive method for confirming grubs is the “pull test.” Because grubs chew off the roots just beneath the soil surface, heavily infested turf will not be anchored. You can easily pull back the grass like a loose carpet, revealing the grubs feeding in the top few inches of soil. Healthy turfgrass can tolerate a small number of grubs, but damage usually appears when populations exceed five to ten grubs per square foot.
Other indicators of a grub problem are signs of animal activity in the lawn. Skunks, moles, raccoons, and birds are natural predators that dig up the turf to feed on the grubs. This foraging behavior creates additional, often severe, damage to the lawn surface, resulting in dug-up tunnels and scattered clumps of grass.
Management and Prevention Strategies
Effective management of white grubs combines long-term prevention with targeted treatment. Maintaining a healthy lawn through appropriate cultural practices is the first line of defense, as strong, vigorous turf can tolerate a higher grub population without showing damage. This includes setting the mower height higher, as longer grass blades encourage deeper root growth, making them less susceptible to grub feeding.
Deep, infrequent watering promotes robust root systems, which better withstand feeding damage. Adult beetles are attracted to consistently moist soil surfaces for egg-laying, so reducing irrigation during the mid-summer egg-laying period can help deter them. Proper soil aeration and thatch management also contribute to overall turf health.
Targeted treatments often utilize biological control agents, which are safer for the environment.
Biological Controls
Beneficial nematodes, specifically Heterorhabditis bacteriophora, are microscopic roundworms that parasitize and kill the grubs. These must be applied when soil temperatures are warm and immediately watered in, ideally in late summer when young grubs are most vulnerable. Another biological option is milky spore disease, caused by the bacterium Paenibacillus popilliae. This disease is effective only against Japanese beetle grubs and can take several seasons to establish control.
Chemical Controls
Chemical controls are categorized as either preventative or curative. Preventative insecticides, such as products containing chlorantraniliprole, are applied in late spring or early summer and remain active in the root zone to kill grubs as they hatch. Curative treatments, often using contact-acting ingredients, are applied in late summer or early fall after damage is noticed. These treatments are designed to kill the larger, actively feeding grubs. Always read product labels to ensure correct application timing, as applying the wrong product at the wrong time can be ineffective.