How to Kill and Prevent Japanese Beetles and Grubs

By Jolene Hansen

Japanese beetles are destructive pests that deliver a two-for-one blow to landscapes and lawns. In their adult form, these invasive Asian natives skeletonize leaves, devour flowers and impair plants. In their larval stage, Japanese beetles are white grubs that feed on grass roots and send lush lawns spiraling downward. By targeting this pest at both stages, you can get rid of Japanese beetles and get your lawn and landscape back on track.

Japanese Beetle Life Cycle: Eggs, Larvae and Adults

Understanding the Japanese beetle life cycle can help you get rid of these pests efficiently and effectively. Adult Japanese beetles emerge from the soil in late spring. About 1/2 inch long when mature, Japanese beetles have bronze wings and metallic green bodies dotted with six small tufts of white hair along each side.

From late spring to midsummer, female beetles target sunny, well-irrigated lawn areas. Then they tunnel into soil and lay eggs about three inches deep. This happens multiple times until they lay up to 60 eggs each.1 The eggs hatch into immature larvae, better known as grubs, about two weeks later.

Japanese beetle grubs feed close to the surface as they pass through several stages, each more destructive than the last. In their final stage, the plump white grubs measure about 1 inch long.

When fall arrives, grubs move deeper underground where they're protected from winter freezes and pesticides. In spring, they move up and feed for a few weeks again. Then they stop feeding, transform into adults, and start the cycle again.

Japanese Beetle Damage: Grubs and Beetles

Adult Japanese beetles feed heavily during the 30 to 45 days after they emerge.2 Few native predators eat these invasive pests. Some plants, such as roses, are favorite targets, but Japanese beetles feed on more than 300 plant types. No plants are guaranteed to repel these pests.

These chewing insects leave distinctive leaf holes. They eat foliage down to the leaf veins, so only a leaf skeleton remains. Swarms converge to feed together, intensifying the damage inflicted on their targets.

Japanese beetle larvae feed heavily from midsummer to early fall. The damage worsens as the grubs grow larger and hungrier. By late summer, large brown patches appear in well-irrigated, well-maintained lawns. Without solid roots, turf feels soft and squishy underfoot and rolls back like a rug. Exposed grubs curl into tight "C" shapes when disturbed.

Heavy grub infestations attract wildlife that feast on these plump pests. Large numbers of starlings or other birds damage grub-infested lawns as they poke and retrieve their meals. Nighttime visitors such as skunks, raccoons, opossums and armadillos leave grub-damaged turf in piles after their feeding expeditions.

Japanese Beetle and Grub Prevention and Control

Japanese beetle control demands a two-fold approach: targeting the beetle's life stage and timing treatment for maximum results. Effective prevention and control require Japanese beetle pesticides that stop the beetle's life cycle and prevent new generations from hatching or maturing to adulthood.

Deterrents such as neem oil simply route beetles to nearby plants and leave them free to reproduce. Japanese beetle traps can lure more of these damaging pests to your yard. But traps only catch an estimated 75% percent of the beetles they attract.1

  • Treat adult Japanese beetles with Amdro Quick Kill Insect Killer for Lawn & Landscape Concentrate or Amdro Quick Kill Insect Killer for Lawn & Landscape Ready To Spray at the first sign of emerging adults in spring — before they damage plants and lay eggs in lawns.  These easy-to-use products work in minutes to kill existing Japanese beetles by contact. Then they continue protecting plants against new beetles for up to three months.
  • Treat Japanese beetle grubs in mid- to late summer when the larvae are close to the surface — before damage intensifies and they go deep for winter. Treat again in spring when grubs return to the surface and new adults emerge. Used as directed, Amdro Quick Kill Lawn Insect Killer Granules II kills beetles and grubs at and below the surface. Your lawn stays protected for up to three months.
  • Using proper timing and effective products breaks the cycle of Japanese beetle damage and prevents new generations of these invasive pests. With Amdro Quick Kill products on your side, you can get rid of Japanese beetles and enjoy beautiful landscapes and lush, green lawns again.

Always read product labels thoroughly and follow instructions.


1. U.S. Department of Agriculture Animal and Plant Health Inspection Service, "Managing the Japanese Beetle: A Homeowner's Handbook," U.S. Department of Agriculture.

2. New York State Integrated Pest Management Program, "Grubs in Your Lawn? A Guide for Lawn Care Professionals and Homeowners," Cornell University.