Lawn grubs are the larval stage of scarab beetles, such as the Japanese beetle, European chafer, and June beetle. These white, C-shaped pests live just beneath the soil surface, where they feed on grass roots. This root destruction prevents the turf from absorbing necessary water and nutrients, leading to visible damage across the lawn. Patches of dead grass can quickly ruin the appearance and health of the yard.
Confirming a Grub Infestation
The first sign of a grub problem is often irregular brown patches that do not green up even after watering. These damaged areas may feel spongy or soft underfoot because the root system holding the turf to the soil has been severed. A simple “tug test” can confirm the issue, as heavily infested turf will easily roll back like a piece of carpet. Secondary damage from animals like skunks, raccoons, or birds digging up the lawn in search of a meal is another strong indicator of a high grub population.
To confirm the severity of the infestation, sample a one-square-foot area by cutting and peeling back the turf. Inspect the soil and root zone for the presence of larvae. Finding five or fewer grubs per square foot is considered a tolerable level for a healthy lawn. If the count exceeds ten grubs per square foot, or if the lawn is already showing significant damage, treatment is warranted to prevent further turf loss.
Chemical Control Methods
Chemical treatments offer two approaches to managing grub populations: prevention and cure. Preventative treatments are applied before the grubs hatch, creating a protective barrier in the soil. Common active ingredients include neonicotinoids like imidacloprid or clothianidin, which are systemic and move into the grass roots where the grubs feed. These insecticides are effective at eliminating newly hatched, small grubs and are used for long-term control.
Curative treatments are faster-acting and are used when an active infestation is causing visible damage. These products typically contain active ingredients such as trichlorfon or carbaryl, which kill the larger, actively feeding grubs on contact. Curative applications are generally less effective than preventative ones because the grubs are larger and harder to eliminate. For both types of control, the product must be watered into the soil immediately after application to move the active ingredient down to the root zone. Always follow the product label instructions to ensure safety and maximize effectiveness.
Biological and Organic Solutions
Several biological and organic options are available to control grubs. Beneficial nematodes are microscopic, soil-dwelling roundworms that parasitize grubs by entering their bodies and releasing a lethal bacterium. The species Heterorhabditis bacteriophora is effective against white grubs. Nematodes must be applied when the soil is moist and temperatures are moderate, followed by immediate watering to help them move through the soil.
Milky Spore is another biological control, consisting of the naturally occurring bacterium Paenibacillus popilliae. This product specifically targets Japanese beetle grubs, causing a fatal disease when ingested. Milky Spore is slow to establish and may take several seasons to build effective concentrations, but it can provide many years of control once established. Maintaining a healthy lawn through cultural controls, such as deep, infrequent watering and mowing at a higher height, makes the turf less attractive for egg-laying beetles.
Optimal Timing for Treatment
Timing is crucial for successfully eliminating grubs, as treatment must align with the pest’s life cycle. Adult beetles lay eggs in the soil during the summer, and the eggs hatch into small grubs in late summer. These young grubs are the most vulnerable stage because they are small, actively feeding near the soil surface, and susceptible to insecticides.
The optimal window for applying most treatments, both chemical and biological, is late summer to early fall, generally mid-August through September. Preventative chemical treatments are best applied earlier in the summer, around June or July, ensuring the active ingredient is present when the eggs hatch. Treating in the spring is less effective because the grubs are larger, have already caused most damage, and are preparing to move deeper into the soil to pupate. Targeting the small, newly hatched grubs in the late summer provides the best chance for control and prevents significant damage.