White grubs are the larval stage of various beetles, including Japanese beetles and masked chafers, and they cause significant damage by feeding on grass roots beneath the soil surface. Effective management depends almost entirely on precise timing related to the insect’s life cycle. Understanding when these pests are most vulnerable allows homeowners to apply the appropriate product at the optimal moment, maximizing control and minimizing the amount of chemical needed. This strategic approach ensures the treatment intercepts the grubs before they have a chance to feed heavily and destroy the turf.
What Are Grubs and How Do I Know I Have Them?
Grubs are soft-bodied, C-shaped larvae that dwell just beneath the soil, typically spending one year in this damaging stage. They sever the roots that anchor the turf to the ground, which leads to patches of dead, brown grass that appear in the late summer or early fall. A telltale physical sign of a severe infestation is turf that can be easily rolled back like a piece of loose carpet because the root system has been eaten away.
The lawn may also feel spongy when walked upon, even before the brown patches become obvious. Secondary indicators of a grub problem often involve wildlife activity, as animals like raccoons, skunks, and birds will dig into the lawn to feed on the large, mature grubs. Digging up a small section of turf can confirm the presence of grubs, and treatment is recommended if you find an average of six or more grubs per square foot.
The Best Time for Preventative Grub Control
Preventative control is the most effective and long-term strategy for managing grubs, as it targets the newly hatched, young larvae before they cause visible destruction. The best timing for this application is generally mid-summer, spanning from late June through early August, which coincides with the period after adult beetles lay their eggs and the larvae begin to hatch. Products containing active ingredients like imidacloprid or clothianidin must be present in the soil when the tiny grubs start feeding.
A product containing chlorantraniliprole has a wider window of application because it takes longer to activate and move into the root zone. This type of preventive treatment can be applied earlier, from late April to early June, ensuring the chemical is fully established in the soil when the grubs hatch in July. Applying any preventative product too early in the spring may allow the chemical to break down before the grubs arrive, making the treatment ineffective.
Timing for Curative (Immediate) Grub Control
Curative treatment is a reactive measure used when turf damage is already apparent, typically in late summer or early fall (August to September), or in the spring. These treatments are designed to kill larger, actively feeding grubs and contain fast-acting ingredients like trichlorfon or carbaryl. Curative products are necessary because the preventative chemicals are not strong enough to eliminate the larger, more established third-instar grubs.
If damage is spotted in the fall, applying a curative product when the grubs are still feeding near the surface can stop further harm before they tunnel deeper for winter. Curative treatments can also be applied in early spring, usually before mid-May, when the grubs move back up to feed before they pupate. While spring application may not save the already damaged grass, it prevents the grubs from maturing into egg-laying adult beetles, helping to break the life cycle.
Essential Steps After Application
The efficacy of any grub control product, whether preventative or curative, is highly dependent on immediate post-application actions. The most important step is to water the lawn immediately after spreading the granular product. This irrigation is necessary to dissolve the insecticide and move the active ingredients down into the root zone, where the grubs are feeding.
A thorough watering of at least one-half inch of water is recommended to drive the chemical deep enough into the soil. Follow the product label instructions regarding re-entry, often waiting until the treated area is completely dry before allowing pets or children back onto the grass. For areas that were severely damaged, follow-up care such as reseeding or overseeding is required to help the lawn recover.