White grubs are a common and destructive pest, representing the larval stage of various scarab beetles, including the Japanese Beetle, the European Chafer, and the May or June Beetle. These creamy-white, C-shaped larvae spend a significant portion of their lives underground, where they chew through and consume the tender roots of turfgrass. When white grub populations become numerous, their feeding severs the root system, preventing the grass from absorbing water and nutrients, which results in large, dead patches in the lawn. Addressing this infestation requires a strategy that aligns with the pest’s life cycle and utilizes both non-chemical and targeted chemical methods.
Identifying the Pest and Optimal Treatment Timing
Confirming a grub infestation involves looking for physical signs of damage, which often appear as irregular brown patches of turf that do not recover with watering. An infested area will feel soft and spongy when walked upon because the roots anchoring the soil are gone. In cases of heavy feeding, the sod can be easily rolled back like a piece of carpet, revealing the grubs feeding beneath the surface. The presence of animals such as skunks, raccoons, or moles digging up the lawn can also signal a grub problem, as these animals forage for the protein-rich larvae.
The life cycle of the most common turf-damaging species is typically one year, beginning when adult beetles lay eggs in the soil during early to mid-summer. The eggs hatch into small larvae, or first instars, in late summer. Treating in late summer or early fall, typically August through September, is the most effective time because the young grubs are small, actively feeding close to the soil surface, and vulnerable to control products. Once the grubs grow larger or move deeper into the soil to overwinter, they become significantly harder to kill.
Non-Chemical and Biological Control Methods
Biological controls rely on natural enemies to manage the pest population without using synthetic chemicals. One effective option involves beneficial nematodes, which are microscopic, soil-dwelling roundworms that actively seek out and infect grubs. The species Heterorhabditis bacteriophora is recommended for white grub control because it is a “cruiser” that actively burrows through the soil to find its host.
Once a grub is located, the nematode enters the body and releases a symbiotic bacterium that quickly kills the pest, often within 48 hours. For successful application, the soil must be kept moist before and after treatment so the nematodes can move freely into the root zone. Apply the product during overcast conditions or in the evening to prevent sunlight and heat from harming the organisms. Immediate watering-in is required to wash them into the soil.
Milky Spore contains the naturally occurring bacterium Paenibacillus popilliae, specifically targeting Japanese beetle grubs. When grubs ingest the spores, they develop a fatal disease known as milky disease. This method is slow to establish, often requiring two to three years of application for the spores to build up in the soil. Once established, the spores can remain active for a decade or more, providing long-term control that is harmless to humans and beneficial insects.
Cultural controls make the lawn environment less appealing for egg-laying beetles and more tolerant of minor grub populations. Maintaining a higher mowing height (three inches or more) encourages the grass to develop deeper root systems that can withstand some root feeding. Reducing irrigation during the peak egg-laying period in July can cause newly laid eggs to dry out and die. Watering deeply and infrequently also promotes deeper root growth, making the turf less susceptible to damage.
Synthetic Chemical Treatment Options
Chemical control is divided into two distinct strategies: preventative and curative, which rely on different active ingredients and application timings. Preventative treatments are designed to be applied before the eggs hatch, ensuring the insecticide is present in the root zone when the young grubs begin to feed in mid-summer. Ingredients like chlorantraniliprole are highly effective, offering long-lasting, systemic protection when applied in early summer, typically mid-June to mid-July.
This prophylactic approach controls the small grubs, preventing damage before it becomes visible. Other preventive options include neonicotinoids such as imidacloprid and clothianidin, which should also be applied in the same early-to-mid-summer window. For all granular or liquid chemical treatments, it is necessary to water the product into the turf with about a half-inch of irrigation immediately after application to move the active ingredient down to the root zone where the grubs reside.
Curative treatments are rescue applications used in late summer or early fall when grub damage is already apparent and feeding is active. These products, which often contain active ingredients like trichlorfon or carbaryl, are fast-acting contact insecticides designed to quickly kill the larger, actively feeding grubs. Curative options have a much shorter residual effect than preventative products, meaning the timing of application must be precise to maximize their impact on the pest.
Because curative applications are typically applied when grubs are larger, they are often less effective than preventative treatments and may not completely halt the damage. Following all label directions is mandatory, especially concerning watering and avoiding application when pets or children are present. Certain neonicotinoid-based products can pose a risk to pollinators, especially if applied when flowering plants are present, so choosing the least harmful option is advisable.