The active ingredient in Scotts GrubEx is chlorantraniliprole, present at a concentration of 0.08%. This insecticide is a preventive grub killer, meaning it works by stopping grub infestations before they damage your lawn rather than eliminating grubs that are already feeding on roots.
How Chlorantraniliprole Works
Chlorantraniliprole targets a specific structure in insect muscle cells called the ryanodine receptor. When the chemical binds to this receptor, it forces calcium to leak out of the muscle cells uncontrollably. The insect’s muscles seize up, it becomes paralyzed, and it dies. This process is primarily triggered when grubs eat treated soil or grass roots, though the compound is also toxic to insect eggs, larvae, and pupae on contact.
The reason chlorantraniliprole is considered a lower-risk pesticide for households with pets and children comes down to biology. The ryanodine receptor in insects is structurally different from the version found in mammals. Chlorantraniliprole binds far more tightly to the insect version, which means it’s highly effective against grubs while posing minimal risk to dogs, cats, and people at labeled application rates.
What GrubEx Targets
GrubEx is designed to kill the larval stage of several beetle species that feed on turfgrass roots. The most common targets include Japanese beetle grubs, European chafer grubs, June beetle larvae, and masked chafer grubs. These white, C-shaped larvae live just below the soil surface and chew through grass roots from midsummer through fall, creating brown patches that peel up like loose carpet. GrubEx also controls other turf-damaging larvae, including those of the black turfgrass ataenius beetle and the Oriental beetle.
When to Apply It
Because chlorantraniliprole is a preventive product, timing matters more than with curative alternatives. You apply GrubEx before grubs hatch and begin feeding, not after damage appears. The standard application window is late spring through early summer, roughly April through mid-June depending on your region. The goal is to get the product into the soil weeks before adult beetles lay eggs in your lawn, so it’s already in place when the tiny larvae hatch and start eating.
Chlorantraniliprole has a long residual life in soil, which is part of why early application works. The compound persists for months, giving it a wide effective window. After spreading the granules with a broadcast spreader, you need to water the lawn with about half an inch of irrigation to move the product off the grass blades and into the root zone where grubs feed. Without watering, the granules sit on the surface and break down from sunlight before reaching the soil.
Preventive vs. Curative Grub Control
GrubEx with chlorantraniliprole is strictly a preventive treatment. If you already see grub damage in late summer or fall, with brown patches lifting easily and grubs visible in the top few inches of soil, GrubEx won’t solve the problem fast enough. The grubs are already too large and actively feeding.
Curative products use different active ingredients, most commonly trichlorfon, which kill larger, actively feeding grubs within days. These are applied in late summer or early fall when damage is present. The tradeoff is that curative insecticides tend to be more toxic to non-target organisms and break down much faster, so they don’t offer season-long protection the way chlorantraniliprole does.
The practical takeaway: if you’ve had grub problems in previous years or live in an area where Japanese beetles and chafers are common, applying GrubEx in spring is the proactive approach. If you missed that window and grubs are already destroying your lawn, you need a curative product instead.
Safety Considerations
Chlorantraniliprole has one of the most favorable safety profiles among lawn insecticides. Its selectivity for insect ryanodine receptors over mammalian ones means it poses very low toxicity to mammals, birds, and earthworms at typical application rates. This is a meaningful distinction from older grub-control chemicals, which were broadly toxic to many organisms.
One area where caution still applies is around water. Chlorantraniliprole can be harmful to aquatic invertebrates, so avoiding application near ponds, streams, or storm drains is important. The product label also advises keeping granules on the lawn and off hard surfaces like driveways and sidewalks, where rain could wash them into waterways. For pollinators, the risk from a granular soil application is considerably lower than from foliar sprays, since bees don’t typically contact treated soil. Still, avoiding application when clover or other lawn weeds are in bloom adds an extra margin of safety.