Grub damage in lawn: when to treat

White grubs -- the larvae of several scarab beetle species -- are a common cause of irregular dead patches in lawns in late summer and fall. They live in the soil and feed on grass roots, severing the root system until the turf can no longer support itself. Understanding how to count grubs, when.

White grubs — the larvae of several scarab beetle species — are a common cause of irregular dead patches in lawns in late summer and fall. They live in the soil and feed on grass roots, severing the root system until the turf can no longer support itself. Understanding how to count grubs, when damage thresholds matter, and how to tell grub damage from other causes prevents unnecessary pesticide applications and missed treatment windows.

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White grub identification

Per Penn State Extension, white grubs are the larval stage of several scarab beetles. They are white to cream-colored, C-shaped, with a tan or brown head capsule and three pairs of legs at the front. They range from 0.5–1.5 inches depending on species and developmental stage.

Common species

**Japanese beetle (Popillia japonica):** Per Rutgers NJAES, the most economically damaging turf grub in the northeastern United States. Third-instar grubs are 1–1.25 inches. The species can be identified from the larva using the "raster pattern" — the arrangement of spines on the underside of the last abdominal segment. Japanese beetle has a V-shaped pattern of spines. This detail requires a hand lens.

**European chafer (Rhizotrogus majalis):** Slightly smaller than Japanese beetle grub. Per Cornell Cooperative Extension, European chafer has become the dominant turf grub pest in western and central New York, often replacing Japanese beetle in that geography. The raster shows two parallel rows of spines.

**Oriental beetle (Anomala orientalis):** Common in the mid-Atlantic and Northeast. Slightly smaller grub. Per Rutgers NJAES, it causes similar root damage but adult beetles do not feed on plant foliage above ground (unlike Japanese beetle adults, which are significant foliage feeders).

**May/June beetles (Phyllophaga spp.):** Native grubs with a 3-year life cycle. Per Penn State Extension, May/June beetle grubs are larger (up to 1.5 inches) and may be present in soil without causing damage until the third year when they are large and have the appetite to match.