Grubs are the larval stage of various beetles, including Japanese beetles and June bugs, which live beneath the soil surface. These pests cause severe damage by feeding on the fine roots of grass, disconnecting the turf from its water and nutrient source. An infestation quickly transforms a healthy lawn into brown, dying grass that fails to recover even with regular watering. Addressing this requires accurate identification, elimination, and turf restoration.
Identifying Grub Damage and Pests
The first indication of a grub problem often appears as irregular, brown patches of grass that do not green up after irrigation, typically beginning in late summer or early fall. The turf may feel spongy or soft underfoot because the root system is being consumed. In severe cases, the grass can be lifted easily like a loose carpet because the roots holding the turf to the soil have been eaten away.
To confirm an infestation, use the “shovel test.” Cut out a one-square-foot section of grass and soil to a depth of two to four inches and examine the soil and exposed roots. The pests are white, C-shaped larvae with a brownish head, usually ranging from one-quarter to one inch long. Finding five or more grubs within that single square foot area is the threshold for needing treatment.
Non-Chemical Cultural Control Methods
Implementing specific lawn care practices makes the environment less hospitable to egg-laying adult beetles and helps the turf tolerate the presence of a few grubs. Adult beetles are attracted to moist soil, so adjusting irrigation practices during mid-summer is beneficial. Watering deeply but infrequently encourages grass to develop deeper root systems, while allowing the topsoil to dry out between waterings deters egg-laying.
Mowing grass at a higher setting, ideally between 2.5 and 3.5 inches, promotes a denser canopy and a larger, more robust root mass. Grass with deeper roots can sustain minor damage from grubs without showing significant stress. Practices like annual core aeration and dethatching also improve soil structure and drainage, which naturally reduces the survival rate of newly hatched larvae.
Applying Curative and Preventative Treatments
The success of any grub treatment depends on precise timing aligned with the grub’s annual life cycle. Preventative treatments target the youngest, most vulnerable grubs shortly after they hatch. These systemic products, often containing active ingredients like imidacloprid or chlorantraniliprole, are absorbed by the grass roots, and the grubs ingest the chemical as they feed.
The optimal time for applying preventative products is typically late spring through early summer (June or July), before the new generation of grubs feeds aggressively. Preventative insecticides must be watered into the soil immediately after application to move the chemical down to the root zone. When applied correctly, these treatments offer a high degree of control and prevent damage before it starts.
Curative treatments are necessary once an active infestation is confirmed and damage is visible, usually from late August through September. These products, which include chemicals such as carbaryl or trichlorfon, are fast-acting, contact-killers applied directly to the active larvae. Curative options are generally less effective than preventative ones, with success rates ranging from 20% to 80% depending on soil conditions and application.
For non-chemical solutions, biological controls offer an effective alternative, though they require careful handling. Beneficial nematodes are microscopic, parasitic worms that actively seek out and infect grub larvae, making them an excellent late-summer curative option. Consistent soil temperature and prompt watering after application are necessary to ensure the nematodes reach the grubs before drying out.
Another biological option is milky spore, a bacterium specific to the Japanese beetle grub applied to the soil. While slow-acting, taking several years to establish, it provides long-term control for up to a decade once the disease is established. Both biological methods are safest for pollinators and other beneficial insects compared to broad-spectrum chemical insecticides.
Repairing the Damaged Turf
Once the grubs are eliminated, lawn restoration begins by addressing dead or thinning grass. First, rake out all dead turf and debris to expose the bare soil and prepare a clean seedbed. This removal process also helps loosen the soil surface, which may have become compacted during the infestation.
Next, the exposed soil should be lightly tilled or aerated. Apply a thin layer of topsoil or starter fertilizer to enrich the area before seeding. Overseeding the damaged patches with a high-quality grass seed mixture is the most economical repair method. Ensure the seed achieves good contact with the soil by gently raking it into the top layer of earth.
Proper post-seeding watering is critical for seed germination and establishment. Keep the newly seeded areas consistently moist with light, frequent watering until the grass seedlings are established. Once the new grass reaches a height suitable for mowing, resume a deep, less frequent watering schedule to encourage a strong, grub-resistant root system.