Lawn grubs are the soft, C-shaped larvae of various beetles, such as the Japanese Beetle and the Masked Chafer. These destructive pests feed aggressively on grass roots, often leading to large, dead patches of lawn that can be rolled back like a carpet. Successful management depends entirely on timing the treatment precisely with the grub’s biological development. Applying the correct product at the wrong time wastes resources and fails to protect the turf.
The Grub Life Cycle and Vulnerability Windows
The life cycle of the common turf-damaging grub spans roughly one year, progressing through four stages: egg, larva (grub), pupa, and adult beetle. Adult beetles emerge in late spring and early summer, laying eggs in the turfgrass, typically between June and August. The eggs hatch into tiny, first-stage larvae within two to three weeks.
These newly hatched grubs immediately begin feeding on the fine roots near the soil surface. This period, from late summer through early fall (August to October), is the grub’s most destructive and vulnerable phase. As temperatures drop, the grubs burrow deeper into the soil to overwinter. They briefly resume feeding in the spring before pupating, making them larger and harder to kill with insecticides.
Applying Preventative Treatments
The most effective strategy for grub control involves a preventative application, targeting grubs when they are newly hatched and small. This approach uses long-lasting, systemic insecticides that must be applied before the eggs hatch in mid-summer. Preventative products containing active ingredients like imidacloprid, thiamethoxam, or clothianidin are typically applied in June or early July. This timing allows the chemical to be absorbed by the grass roots, creating a toxic zone for the larvae when they begin to feed.
An alternative preventative ingredient is chlorantraniliprole, which offers a wider application window, allowing for application as early as April or May. Since this chemical takes longer to fully activate in the root zone, earlier spring application is often more effective than application closer to the summer hatch. Preventative treatments eliminate the next generation of pests and are not effective against the larger, mature grubs found in the spring or late fall.
Applying Curative Treatments
Curative treatments are necessary when preventative measures were missed or failed, and active grub damage is visible in the lawn. Damage is typically seen in the late summer or early fall (August through October), when the grubs are larger and actively feeding near the surface. Signs of infestation include brown, wilted patches of grass, a spongy feel underfoot, or turf that pulls up easily because the roots have been severed.
These situations call for fast-acting, contact insecticides containing active ingredients such as trichlorfon or carbaryl. These chemicals are designed to kill the larger, existing grubs quickly. For maximum efficacy, products should be applied promptly after damage is confirmed and while the grubs are still feeding. Applying curative chemicals too late in the fall, past October, may be ineffective as the grubs burrow deep to prepare for winter. Curative treatments are also the only option if a high number of grubs is found in the spring before early May.
What to Do After Grub Control
Regardless of the product used, activating the chemical with water immediately after application is necessary. The insecticide must be carried down through the thatch layer and into the soil to reach the root zone where the grubs are feeding. A recommended amount is about 0.25 to 0.5 inches of irrigation, which can be accomplished with a lawn sprinkler.
After the treatment is watered in, monitoring the lawn for continued signs of grub activity is important. Curative treatments should show effects within a few days to a week, though some products may take longer to eliminate pests. If damage has occurred, the dead patches should be repaired through overseeding or patching to restore turf density and prevent weed invasion.