Heterorhabditis bacteriophora
Grub nematode (Hb)- Rate
- 250k–500k /m²
- Temp
- 12–35 °C soil (sources vary)
- Best for
- Curative drench in late summer, moist soil
Pest
White grubs
Scarabaeidae (Popillia, Cyclocephala, Rhizotrogus, Phyllophaga)
The short answer
Lawn grubs are the C-shaped white larvae of scarab beetles: in the northern and eastern United States mainly Japanese beetle, masked chafers, European chafer and May/June beetles. They chew off grass roots just below the surface. The first sign is usually brown patches in late summer that lift like a loose carpet, or skunks, raccoons and birds tearing up the turf to eat them. Before treating, count them. Cut out a square foot of turf in several places. Extension services treat 5–10 grubs per square foot as the point where control is worth it, depending on the species.
hero macro · C-shaped grub in turf roots
A third-instar white grub in the root zone of peeled-back turf. Photo: pending.
Identification
All lawn grubs look alike at first glance: a stout, greyish-white, C-shaped body with a brown head and three pairs of legs, curled up at rest. Depending on species, mature grubs range from about 1/4 inch to 2 inches (roughly 6 mm to 5 cm). Kentucky gives 3/8 to 2 inches and Purdue 1/4 to 1½ inches for older larvae. Size alone will not tell you the species, and the species matters, because each one tolerates different numbers and times its damage differently.
The tell is on the underside of the last body segment, called the raster, and you need a 10× hand lens to see it. Japanese beetle grubs have a V-shaped pattern of spines and a tan head. Masked chafer grubs have a scattered pattern and a chestnut head. European chafer grubs have two parallel rows of spines and a Y-shaped anal slit. The adults are easier: Japanese beetles are metallic green, masked chafers are brown, about 1/2 inch long and fly over the turf at dusk, European chafers are tan and about 1/2 inch long and swarm around trees at sunset in June and July, and May/June beetles are solid brown and 3/4 to 1 inch long.
Easily confused with
- Billbug larvaeAlso a pestCream-white with a brown head like a white grub, but legless and only 1/4–1/2 inch long. White grubs have three pairs of legs and grow larger.
- Black vine weevil grubsAlso a pestC-shaped and white with a brown head, but legless, and found among the roots of pot plants and shrubs rather than under lawn turf. White grubs have three pairs of legs.
Damage symptoms
Grubs chew off roots just below the surface, so the turf cannot take up water and gives up first in hot, dry weather. Damage from the annual species shows in late August and September, when the grubs are large and feeding hard, and less often in spring. Many brown patches are not grubs at all. Kentucky Extension's test is simple: if the brown turf does not pull up easily, look for another cause first, such as a dry spot, dog urine, fertiliser burn, buried rock or disease.
- Thinning and yellowing, then irregular dead patches that grow
- Turf that feels spongy underfoot and peels back like a carpet, with few roots left
- Sudden wilting in turf that looked healthy, in hot, dry weeks
- Skunks, raccoons or birds digging up the turf; moles tunnelling
- Brown adult beetles skimming the turf at dusk or crowding round porch lights in early summer
Lifecycle & degree days
Japanese beetle, masked chafers and most European chafers take a year. Adults emerge from the soil in early summer, lay eggs in the lawn, and the eggs hatch in about two weeks. The grubs grow through late summer, go deeper when the soil cools in October and November, come back up to feed in spring, and pupate in late May. That cycle sets the two treatment windows. May/June beetles take two to three years, so their grubs can be in the soil all season.
- Generations
- 1 a year (Japanese beetle, chafers); 2–3 years (May/June beetles)
- Eggs laid
- Late June to early August, in Kentucky
- Egg hatch
- About 2 weeks (Japanese beetle 10–14 days, masked chafer 14–21, European chafer 2–3 weeks)
- Damage shows
- Late August to September; spring less often
- Preventive window
- Mid-May to July, before egg hatch — timing varies by product
- Curative window
- Late July to mid-September, while grubs are small
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Host crops
White grubs prefer grass roots but also feed on the roots of other plants, including weeds. The worst-hit lawns tend to be in full sun on south- or west-facing slopes, sown with Kentucky bluegrass, heavily watered in June and July (which draws egg-laying females), or damaged by grubs the year before. Kentucky Extension suggests renovating badly damaged bluegrass or ryegrass lawns with tall fescue, which tolerates grubs better.
Monitoring & action thresholds
Action threshold
5–10 grubs per ft²
That is roughly 54–108 per m². It depends on the species: UMass gives May beetle 2–4, European chafer 3–8, masked chafer 6–15, Japanese and Oriental beetle 8–15, and Asiatic garden beetle 12–20. Purdue gives European chafer 5 and Japanese beetle 10 or more. Irrigated turf tolerates more: Kentucky Extension says it can sometimes carry 20 or more per ft² before injury shows.
Sample in August or early September, before injury shows. In several places, cut a square foot of turf on three sides, fold it back, and count the grubs in the roots and the top 2 inches (5 cm) of soil. The Northeastern IPM Center suggests at least 10 spots, 10–20 feet (3–6 m) apart, walked in a zigzag. With a golf cup cutter, multiply the grubs per core by 10 to get the count per square foot. Tamp each sample back and water it. Digging animals are a hint but not proof: moles also eat earthworms, and killing grubs does not stop them.
Beneficial
Biological control
No biological product controls grubs as reliably as the soil insecticides. That is the verdict of Kentucky Extension, and nursery trials in Tennessee put biological treatments at 0–75% control of young Japanese beetle grubs. The insect-killing nematode Heterorhabditis bacteriophora is the biological option extension services point to, and it works best on moist soil in late summer. Sources differ on how well: Ohio State says it can match the standard insecticides against Japanese beetle grubs, while Minnesota and Kentucky call its results inconsistent. Wild enemies help in the background: Tiphia wasps parasitise Japanese beetle grubs, ants and ground beetles take eggs and young grubs, and rove beetles are among the predators recorded killing many Japanese beetle eggs and young larvae. Milky spore infects Japanese beetle grubs only and has performed poorly in Kentucky trials. It does nothing to chafer or May beetle grubs.
Carabidae
Ground beetles- Kind
- Wild — attract it
- Best for
- Background predation on eggs and young grubs
Staphylinidae
Rove beetles- Kind
- Wild — attract it
- Best for
- Background predation on Japanese beetle eggs and young grubs
Cultural controls
Watering is the lever in both directions. Watering in June and July attracts egg-laying beetles and helps the eggs survive. In August and September, when the grubs are feeding, good soil moisture hides root loss and helps the turf recover. Deep, occasional soaking is better than frequent light watering.
- Count before you treat — only a small share of lawns needs treatment in any year
- Avoid heavy watering in June and July if the lawn has had grubs before
- Water deeply in late August and September to carry turf through the feeding period
- Feed moderately in autumn rather than heavily in spring and summer
- Rake out thatch before any treatment, and water it in with 1/2–1 inch (13–25 mm) of water straight after
- Renovate badly damaged bluegrass or ryegrass with tall fescue
Chemical, last resort
Preventive products (neonicotinoids, chlorantraniliprole) go on before egg hatch. Curative ones (trichlorfon, carbaryl) should wait for a count. Minnesota Extension rates the neonicotinoids, trichlorfon and carbaryl as risks to bees, and chlorantraniliprole as low risk. Follow the label.Check any product before it goes on. Open the compatibility matrix →
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
Univ. of Kentucky ENT-10, Controlling White Grubs in Turfgrass (M.F. & D.A. Potter, 1999)
Purdue Extension E-271, Managing White Grubs in Turfgrass (Richmond, 2023)
Penn State Extension, White Grubs in Home Lawns (Heller, updated 2026)
UMass Extension, Turf BMPs Section 11: Insect Management (threshold table)
UMass Extension, Current Insecticide Approaches for White Grub Control (Vittum, rev. 2013)
Northeastern IPM Center, White Grubs (school IPM best practices)
Ohio State Ohioline ENT-0107, White Grub Identification, Biology and Management (2026)
Cornell Cooperative Extension, European Chafer fact sheet (Klass, updated 2009)
Potter & Held, Biology and Management of the Japanese Beetle, Annu. Rev. Entomol. 47:175–205 (2002)
Mannion et al., Management of early-instar Japanese beetle…, J. Econ. Entomol. 94:1151–61 (2001)
Univ. of Minnesota Extension, Japanese beetles in yards and gardens (2025)
BASF, Nemasys G technical information bulletin (2013)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →White grubs by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.