Grubs are the C-shaped, white larvae of various scarab beetles, most commonly the Japanese beetle or the masked chafer. These pests live beneath the soil, where they consume grass roots, eventually leading to large, dead patches in the turf. Successful management relies on applying control products at the correct time in the grub’s annual development cycle. Understanding the local seasonal schedule is paramount because treatment effectiveness changes based on the grub’s size and location.
The Grub Lifecycle and Vulnerable Stages
The common white grub in Missouri follows an annual life cycle. Adult beetles emerge from the soil from June through August to mate, with females laying eggs shortly after emergence. These eggs hatch into tiny larvae, or grubs, usually around late July or early August.
The newly hatched grubs immediately begin feeding on grass roots close to the surface, growing rapidly throughout the late summer and fall. As temperatures drop, the grubs burrow deeper into the soil, often 5 to 10 inches down, to overwinter. They become active again in the spring, feeding briefly near the surface in April and May before they pupate and transform into adult beetles, restarting the cycle. The most vulnerable stages are when the grubs are newly hatched in late summer and when they are small and located near the soil surface.
Timing Preventive Applications in Missouri
Preventive control targets grubs while they are in the egg or very early larval stage. This strategy uses systemic insecticides, such as those containing imidacloprid or chlorantraniliprole, which must be absorbed by the grass roots to be effective. These long-lasting products work by poisoning the roots the grubs will later consume.
The optimal window for applying preventive treatments in Missouri is from late May through early July. Application during this time ensures the insecticide is fully distributed throughout the root zone before the eggs hatch in late July or early August. Applying the treatment too early, such as in April, risks the product degrading before the grubs arrive.
Timing Curative Applications in Missouri
Curative control is necessary when an infestation is discovered after damage has already begun. It employs fast-acting products like trichlorfon or carbaryl, which kill the grubs on contact or shortly after ingestion. The effectiveness of curative products depends on the grubs being small and actively feeding near the soil surface.
The best time for curative action in Missouri is late August through September. This aligns with the period when newly hatched grubs are at their smallest and most active feeding stage. Applying treatment during this window maximizes the kill rate, as the grubs are vulnerable and close to the application zone. Curative treatments applied in the spring are significantly less effective because the mature grubs are larger and more resistant.
Recognizing the Need for Grub Control
Identifying the need for grub control involves looking for specific physical signs that distinguish grub damage from other lawn issues.
Indicators of Infestation
- Irregular, brown patches of grass that do not improve with watering.
- The grass in damaged areas often feels spongy underfoot because the grubs have severed the root system.
- Turf can be easily lifted or rolled back like a loose piece of carpet, revealing the white, C-shaped grubs underneath.
- Increased activity from animals like skunks, raccoons, or birds, which dig small holes in the lawn while foraging.
To confirm an infestation, dig up a one-square-foot section of turf to a depth of two to four inches. If the soil sample contains a density of five to ten or more grubs, treatment is warranted.