When moles begin to tunnel through a lawn, creating unsightly mounds and ridges, homeowners often seek a solution that targets the mole’s presumed food source: grubs. This common approach involves applying insecticide to the turf to eliminate the grub population, thereby encouraging the moles to leave the area. However, the success of this strategy depends entirely on understanding the pest life cycle and applying the treatment at the precise moment it will be most effective. The timing of grub control application is the most important factor in preventing the root damage caused by grubs and subsequently reducing the mole’s attraction to the lawn.
Understanding the Grub-Mole Connection
Many people believe that the appearance of moles signals a major grub infestation, but this connection is not as direct as commonly thought. Moles are insectivores whose diet consists primarily of earthworms, which often account for 85% to 90% of their food intake. Earthworms are the mole’s favorite food and main source of water, making them the primary reason moles tunnel through the soil.
While moles consume white grubs and other insects, grubs are a secondary food source. Eliminating grubs through insecticide application may remove a portion of the mole’s diet, but it will not remove the earthworms that sustain them. Grub control is ultimately a turf-protection measure that secondarily aims to make the lawn less attractive to moles by reducing one food source.
The Critical Timing of Grub Control Application
Effective grub control hinges on understanding the annual life cycle of common pests like the Japanese Beetle or European Chafer. Adult beetles lay eggs in the soil during early to mid-summer, typically June and July. These eggs hatch into tiny larvae, known as first-instar grubs, in late summer, usually from late July through August.
The period when these grubs are small and newly hatched is the most vulnerable point in their life cycle and the optimal time for a preventative insecticide application. Applying the treatment from mid-June to mid-July ensures the chemical is present in the soil just as the eggs hatch and the young grubs begin to feed on grass roots. This timing targets the first-instar grubs that are still small and close to the soil surface, resulting in the highest control success rate.
As grubs grow larger into their second and third instars in the late summer and fall, they become progressively harder to kill because they are more robust and require a higher dose of insecticide. Applications made after mid-August, or certainly by the time damage is visibly apparent in September, are far less effective for preventative products. Grub control applied in the spring is ineffective because the grubs are already mature, have moved deeper into the soil for winter, and will soon stop feeding to pupate.
Selecting the Right Treatment Type
The choice of grub treatment depends on when the application is made, differentiating between preventative and curative products. Preventative treatments are designed for early application before grubs hatch and typically use active ingredients such as imidacloprid or chlorantraniliprole. These products have a long residual activity, sometimes lasting all season, and must be watered into the soil to reach the root zone where newly hatched grubs feed.
Chlorantraniliprole can be applied as early as April or May because it takes longer to move into the soil but remains active for an extended period. Imidacloprid is best applied closer to the egg hatch in June or July. Preventative treatments offer the most reliable control, often reducing grub populations by 65% to 80%.
Curative treatments are reserved for late summer or fall when damage is visible and the grubs are larger. These products, which include active ingredients like trichlorfon or carbaryl, are fast-acting but have a short residual life, requiring precise timing to hit the feeding grubs. Curative applications are generally less effective than preventative measures, with control rates sometimes ranging from 20% to 80% depending on the specific timing and grub size. Once a treatment is applied, it is essential to water the area with at least a quarter to half an inch of water to move the chemical down to the grubs’ location.
Alternative Methods for Mole Management
Since eliminating grubs will not remove the earthworms that moles prefer, homeowners should consider direct control methods for persistent mole activity. Trapping is the most effective and reliable physical method for controlling mole populations. The process involves locating active tunnels, which are re-used daily, and strategically placing specialized mole traps, such as harpoon or scissor traps, within these runways.
Another alternative is the use of chemical baits, formulated to mimic the mole’s primary food source, the earthworm, which are placed directly into the active tunnels. Physical exclusion can also be utilized for high-value areas, involving the installation of underground fencing or wire mesh barriers extending at least a foot deep into the soil. Repellents containing unrefined castor oil can be applied to the lawn, as the strong odor and taste encourage moles to relocate.