Best Grub Killer: Two Actives, and One Aisle Full of Wrong Ones

Count first: the threshold

This is the only buying guide on this site whose first recommendation is frequently to buy nothing, and the reason is a number. Penn State’s threshold:

If an average of five grubs per square foot or more is found in non-irrigated turf, or fifteen or more per square foot in an irrigated lawn, an insecticide application may be desirable.

The irrigated figure being three times higher is the important detail. A watered lawn replaces roots faster than the larvae remove them, so the same grub population that ruins a dry lawn is invisible in a maintained one. Which means the honest first step is a trowel, not a bag: cut and fold back a square foot of sod in three or four places across the lawn and count what is underneath.

Our lawn grubs guide covers the counting method and the damage patterns that are actually grubs rather than drought, billbug or dog urine.

The two actives that work

Grub control is not one job. It is two jobs several months apart, and each has its own molecule.

Chlorantraniliprole — the preventive. MSU: most effective applied in May or June. It goes into the soil before the eggs hatch and is still present when the young larvae begin feeding. It also picks up surface feeders — sod webworm and cutworm — as a secondary benefit.

Trichlorfon — the curative. MSU: most effective in late August or early September, against grubs already feeding. This is the emergency option, and it should be bought with realistic expectations, because MSU has measured them:

Curative treatments will kill “20–80% of grubs when applied in September or 20–55% when applied in late October.”

That range is why the preventive route exists at all. MSU’s own framing of the trade-off is worth keeping: the curative approach “avoids unnecessary applications of chemicals, but is not as effective as preventive products.” Both halves of that sentence are true, and which half matters more depends on whether your lawn has a grub history.

Our grub preventer vs grub killer guide works through that decision in more detail.

The actives that do not work

Here is the sentence that should reorganise this aisle. MSU Extension:

Products containing only lambda-cyhalothrin, gamma-cyhalothrin, bifenthrin, deltamethrin, cyfluthrin or permethrin “should not be used for any phase of grub control.”

Those are pyrethroids. They are genuinely effective insecticides — against insects on the surface. They bind tightly to organic matter and thatch and do not move down into the root zone where grubs live, so the grub never meets the chemical.

The problem for a shopper is that the bag does not say this. At least one widely sold product pairs lambda-cyhalothrin with the words Season Long Grub Control on the label. It is not a counterfeit and it is not mislabelled in a regulatory sense — it is simply a surface insecticide sold for a subsurface pest, and it is the reason our own review of it sits below 3 out of 5.

If you take one thing from this page to the shop: turn the bag over and read the active ingredient. If the only active is on MSU’s list, put it back regardless of the name on the front.

The picks

Two things about that second card are worth reading before you buy it. We read its EPA label (reg. 92564-40) and the registered product name is Dylox 9.3% Insect Granules — the BioAdvanced name is an alternate brand name on the same registration, so the retail bag is Dylox rather than a lookalike. And the label carries a restriction most people would breach without noticing: “Do not apply with hand-held or chest mounted spreader.” On a small lawn that is the applicator many people own, so check what you are spreading it with before ordering.

Before you buy, two local checks

Your state may have removed an option. Vermont has prohibited applying neonicotinoid pesticides to turf since July 1, 2025, which takes the imidacloprid and clothianidin season-long products off the table there. That is the sharpest example, but state pesticide rules differ more than most people expect — our state pages carry the local position.

Your species may not be the label’s species. European chafer stays in the root zone later in autumn and returns earlier in spring, which moves the treatment window away from the printed calendar. Oriental beetle, which dominates Connecticut, Rhode Island and coastal Massachusetts, does not answer to every product sold for grubs. Identifying what you dug up is not pedantry here; it changes both the timing and the product.

Grubs in Delaware

Delaware's own pest record names the larvae you are likely to dig up: White grubs — Japanese beetle and masked chafer, and the sandy Sussex soils make egg-laying easy.

Masked chafer is the annual white grub, and that simplifies your calendar. One generation a year: eggs in midsummer, larvae feeding on roots through late summer, damage showing in Delaware as the lawn comes out of summer stress. The label calendar is written for this insect, so the printed windows apply — May or June for the preventive, late August or early September for the curative. And the adults do nothing above ground, so if something is chewing your ornamentals as well, that is a different beetle and a different problem.

Which threshold applies to your lawn. Penn State's five per square foot is the unirrigated number and fifteen is the irrigated one, and Delaware's rainfall decides which one you are reading: Roughly 45 inches, fairly even, with thunderstorm-driven summer peaks that run straight off clay in the north and straight through sand in the south. Most lawns here run on rainfall for much of the season, which puts you nearer the five-per-square-foot bar than the fifteen. If you do irrigate through the dry weeks, use the higher number for the part of the season you are watering.

What else is in Delaware that looks like grub damage. The state's pest record also carries Chinch bugs (hot dry sand along drives, walks and the beach-town lots); Sod webworm; Billbugs; Fall armyworm in late-summer outbreak years; Mole crickets at the far southern edge, where the coastal plain starts behaving like the mid-Atlantic South. Every one of those thins turf in irregular patches that lift or brown like grub damage, and none of them is treated with a grub product. The square foot of peeled sod is what separates them — grub damage comes with grubs under it, in countable numbers. Lawn grubs covers the dig, and fungus identification covers the patches that are not insects at all.

The month the eggs go in, and what else you are doing that month. Adult beetles choose moist soil to lay in, which is the mechanism behind the two thresholds above rather than a separate fact: a lawn watered through midsummer is a more attractive egg site than the dry one next door, and it then grows roots fast enough to carry three times the larvae. Delaware's summer conditions — High and persistent — the Delaware Bay and the Atlantic hold night temperatures up through July and August, which is precisely what a cool-season lawn cannot tolerate And the state's own summer list is already busy while that is happening: Expect brown patch on tall fescue and manage it as a nitrogen and watering problem first, a fungicide problem second; Water early morning and deeply; the Sussex sands need more frequent, lighter cycles than the northern clays do. A preventive grub application belongs ahead of that list, not squeezed into it.

What grub damage does to Tall Fescue. The count decides whether to treat; the grass decides what the damage costs. Tall Fescue is a bunch-type grass: it grows from its own crown and does not run sideways to fill a gap. So a grub patch here does not knit closed on its own the way a bluegrass patch does — the repair is reseeding, which is why the threshold matters more on this lawn than on a rhizomatous one. Soil and drainage change how the treatment behaves, and here they are Fast through the Sussex sands, excessively so along the beach ridges, where nitrogen reaches groundwater rather than roots; slow on the New Castle and northern Kent clays, and effectively nil in the tidal marsh muck at the margins — ground that holds water at the surface, which is where a poorly watered-in granule stays. Every grub product has to be irrigated down to the root zone, and on this soil that takes deliberate watering rather than a light sprinkling. Frost bookends the season: first frost Late October in New Castle County; early to mid-November along the Sussex coast, last frost Mid-April statewide, a week or so earlier on the immediate coast. Curative applications lose efficacy as soil cools — MSU's own range drops from 20–80% in September to 20–55% in late October — so the first of those two dates is the deadline the bag does not print.

What Delaware lets you buy. Delaware's recorded chemical restrictions do not name the neonicotinoids, so the season-long imidacloprid and clothianidin products are available here — which is not the same as recommended, since chlorantraniliprole displaced them in retail on both efficacy and bee risk. The authority is Delaware Department of Agriculture: Delaware Department of Agriculture.

The honest summary

The best grub killer for most lawns in most years is no grub killer, because most lawns never reach five grubs per square foot and have never been counted. When the count does clear the bar, the month decides the molecule: chlorantraniliprole in May or June if you are preventing, trichlorfon in late August or early September if you are already losing turf. Everything else in the aisle is either the wrong timing or, in the case of the pyrethroid-only products, the wrong chemistry for a pest that lives three inches down.