Lawn grubs, the c-shaped larvae of beetles like the Japanese beetle or June bug, are a common source of frustration for homeowners. These pests feed aggressively on the roots of turfgrass, which absorb water and nutrients. The destruction of this root system leads to visible brown patches and weak turf that can feel spongy underfoot. This guide covers eliminating the active grub population, repairing the resulting damage, and implementing long-term prevention strategies.
Confirming Grub Activity and Damage Extent
Patches of brown, dying grass that appear in late summer or early fall, even in well-watered areas, are a strong indicator of grub activity. A simple “pull test” can provide quick confirmation: if you can easily lift or roll back a section of the turf like a piece of loose carpet, it indicates that the roots have been severed by feeding grubs.
To determine the severity of the infestation, cut a one-foot square section of turf, approximately two to four inches deep, near the edge of a damaged area. Peel back the square and count the number of C-shaped grubs exposed on the soil surface and clinging to the turf roots. Finding five or fewer grubs per square foot is generally considered a manageable population. However, ten or more grubs per square foot suggests a serious infestation that requires immediate treatment.
Treating the Active Pest Population
Curative insecticides, such as products containing trichlorfon or carbaryl, are fast-acting chemical treatments that kill grubs on contact. These treatments are most effective when applied in late summer or early fall (August through September) when the grubs are actively feeding close to the soil surface. Apply these chemicals strictly according to the manufacturer’s instructions and water them in with about a quarter-inch of water to ensure the active ingredients reach the root zone.
Biological controls offer a slower but effective solution. Beneficial nematodes can be applied to the soil to parasitize and kill the grubs. Milky spore, a natural bacterium specific to Japanese beetle grubs, is also available. These biological agents require moist soil conditions and the correct soil temperature to be most effective.
Curative treatments are most effective against smaller, younger grubs. Waiting until late October or early spring to treat often proves ineffective, as the grubs move deeper into the soil to overwinter and are more resilient. After treatment, re-sample a small section of the lawn a few weeks later to confirm the control measures were successful before proceeding with physical repairs.
Physical Steps for Lawn Restoration
Begin by thoroughly raking the damaged areas to remove all the dead, brown grass and any debris. Removing this thatch and dead material allows for better seed-to-soil contact, which is necessary for successful germination.
The soil must be prepared to receive new seed or sod. Lightly aerate the bare patches using a garden rake or a core aerator, which helps relieve compaction and improves water penetration. If the soil surface is uneven, add a light layer of topsoil or compost to fill in depressions and create a smooth, level seedbed.
Reseeding is the less expensive option for restoration. Select a grass seed blend appropriate for your region’s climate and the specific sunlight conditions of the damaged area. Apply the seed at the recommended rate and lightly rake the area to ensure the seeds are slightly covered by soil, protecting them from birds and drying out.
Sod provides an immediate repair, as pieces can be cut to fit the bare patches precisely. Regardless of the method, press the newly seeded or sodded area to ensure firm contact with the underlying soil. New grass requires frequent, light watering—often two to three times a day—to keep the top layer of soil consistently moist until germination occurs.
Maintaining a Grub-Free Environment
Long-term grub control depends on proactive prevention. Understanding the annual grub lifecycle is important, as adult beetles lay their eggs in the soil during early to mid-summer. Preventative treatments, which contain active ingredients like imidacloprid or chlorantraniliprole, must be applied in early summer before the eggs hatch.
These systemic insecticides are absorbed by the grass roots, creating a barrier that kills the grubs when they begin feeding after hatching. Unlike curative products, these preventative options target the pests when they are small and most vulnerable. Proper timing ensures that the chemical is active in the soil when the young grubs are present.
Cultural practices increase the lawn’s resilience. Mowing the grass at a taller height (three to four inches) encourages deeper, stronger root growth, helping the turf withstand minor root feeding. Additionally, deep, infrequent watering encourages roots to grow downward, making the soil less attractive for adult beetles compared to consistently wet soil surfaces.