Grub killers eliminate the larvae of various beetles, such as the Japanese beetle and June beetle, which are commonly known as white grubs. These C-shaped larvae live beneath the turf surface, feeding voraciously on grass roots and organic matter. This feeding severs the plant from its root system, causing the lawn to develop irregular brown patches that can be easily lifted like a piece of carpet. Grub control is necessary for maintaining a healthy lawn.
The Two Main Categories of Grub Control
The products available to combat lawn grubs fall into two distinct categories based on their origin and mechanism: synthetic chemical controls and natural biological controls. Synthetic controls are man-made insecticides, typically offering either a fast-acting, short-term effect or a longer-lasting, systemic preventative action. These are often the preferred choice for a quick or season-long defense against damaging infestations.
Biological controls use natural enemies to manage the grub population. This category includes beneficial nematodes, which are microscopic roundworms that parasitize the grubs in the soil. Another option is the bacterium Bacillus thuringiensis subspecies galleriae (Btg), which is ingested by the grubs and disrupts their digestive system. Biological options are generally slower to act but introduce no synthetic chemicals.
How Synthetic Grub Killers Attack the Pest
The most common synthetic grub killers, particularly those used for long-term prevention, rely on a class of compounds called neonicotinoids, such as imidacloprid or clothianidin. These chemicals are systemic, meaning they are absorbed by the grass roots after application and move throughout the plant tissue. When a grub feeds on the treated roots, it ingests the insecticide.
The mechanism of action for neonicotinoids is that they act as neurotoxins by binding to nicotinic acetylcholine receptors (nAChRs) in the insect’s central nervous system. This binding overstimulates the nerve cells, leading to paralysis, an inability to feed, and ultimately death. This systemic approach is highly effective because the poison is delivered directly to the grub’s food source.
Curative treatments, used when an infestation is visible, often contain active ingredients like carbaryl or trichlorfon. These chemicals are faster acting and work through both contact and ingestion to kill larger, actively feeding grubs. Trichlorfon, for instance, is a non-systemic organophosphate that disrupts the nervous system by interfering with the enzyme acetylcholinesterase. This rapid action halts damage when mature grubs are causing significant turf destruction.
Timing and Application for Maximum Effectiveness
Applying grub control effectively depends on timing the application to the grub’s annual life cycle. Adult beetles lay eggs in the soil during early to mid-summer; the newly hatched grubs are small, fragile, and feed near the surface in late summer. Preventative treatments, such as those containing neonicotinoids, are optimally applied from mid-June to mid-July so the chemical is in place when young grubs hatch and begin to feed.
Curative treatments are reserved for late summer or early fall when turf damage becomes apparent and the grubs are larger. These quick-acting products rescue the lawn from an active infestation, but they are less effective against mature grubs than preventative products are against younger larvae. Spring treatments are discouraged because grubs briefly move to the surface to feed before pupating, and the grubs are tough. For all applications, the chemical must be watered into the soil immediately after spreading to ensure it moves down into the root zone.
Environmental Impact and Safety Considerations
The widespread use of synthetic insecticides raises concerns regarding their impact on non-target organisms and the environment. Neonicotinoids, while effective against grubs, are highly toxic to beneficial insects, particularly pollinators like bees, if exposed to chemical residue in blooming weeds like clover. They can also negatively affect other soil-dwelling organisms, including earthworms and microarthropods, which benefit soil health.
To mitigate these risks, users should follow all label instructions and avoid applying chemicals to lawns where blooming plants are present. Granular formulations, which are watered in quickly, are preferred over sprays because they minimize dust drift and direct exposure to surface-foraging insects. Water contamination is a risk if chemicals are applied just before heavy rain, leading to runoff into local waterways. Precautions such as storing products in locked areas and keeping pets and people off the treated lawn until dry are necessary for safety.