How to Control Japanese Beetles in Your Lawn and Garden

Japanese beetles (Popillia japonica) were not much of a problem in the United States until about 1919, when this ravenous native of Japan began a serious invasion, probably after hitchhiking to North America on imported ornamental plants. Today, they are a serious nuisance to gardeners and farmers across this continent.

The adult Japanese beetles that eat so many plants are about 3/8-inch long, with a shiny, metallic green body and copper-brown wing covers. However, not all metallic green or copper beetles are Japanese beetles. To ensure you're dealing with Japanese beetles, check their undersides for five small, white tufts under the wing covers and an additional tuft at the end of the abdomen.

Why Japanese Beetles Are a Problem

While individual Japanese beetles aren't a particular threat, these insects tend to hatch in large numbers, and when they congregate on a shrub, tree, or other plants, they can quickly defoliate it.

They run in cycles; some years are almost devoid of beetles, while others are everywhere. When there is an infestation, it is often a huge one that can seriously damage large numbers of plants. The sheer numbers make it hard to eliminate them, but there are still steps you can take to control and prevent Japanese beetles.

There's a vast smorgasbord of plants for Japanese beetles to feast on—more than 300 varieties of trees, shrubs, and non-woody plants. During a year with a serious infestation, gardeners may feel as though there is no plant that the beetles don't enjoy.

Signs of a Japanese Beetle Infestation

• You see one or more hovering or flying Japanese beetles
• Plant damage appears like lacy-looking, skeletonized leaves
• Brown, irregularly shaped dead or brown lawn patches
• Spongy-feeling turf that lifts easily (roots are eaten through)
• Increased presence of birds, raccoons, and other critters digging up the lawn or plant soil to eat grubs

Identification and Development of Japanese Beetles

Beetles typically go through four stages of development: egg, larvae, pupae, and adult. Knowing when they are passing through each stage in your climate is important because control methods differ.

Egg

The mature beetles lay small, oval, white eggs in the soil. If moisture is sufficient, the eggs will absorb it and enlarge, becoming rounder as they do. The eggs develop at different rates in different soil temperatures, developing rapidly in warm soils of about 80 to 90 degrees Fahrenheit. When soil conditions and temperatures are ideal for eggs to hatch, you can expect an infestation of lawn grubs that move up to the surface and start feeding on plant roots and organic matter.

Larvae

Larvae are the white grubs that are so familiar (and damaging) in lawns. Japanese beetle larvae have a V-shaped series of bristles on their underside. Grubs will grow in length as they feed and mature. In large numbers, these grubs can kill off large areas of lawn. Apply pesticide grub control in late summer to fall while the grubs feed on the roots. As the soil cools and the grubs mature, they move back down deeper into the soil for winter.

Pupae

The pupae stage is when the grub starts to transform into a beetle. Japanese beetle pupae start cream-colored and age to reddish-brown. As the soil warms, the larvae burrow toward the surface to change into beetles. The pupating stage lasts about two weeks.

Adult Beetles

Adult beetles are less than 1/2-inch long and have shiny, metallic green shells. Depending on your area, adults emerge from the ground between May and June. When the first beetles emerge, they immediately look for suitable plants and feed. They also send out an odor known as a congregation pheromone to signal later emerging beetles where to go. Mating starts soon after.

Adult female beetles burrow into the soil to lay their eggs, then return to feeding, mating, and repeating the cycle. By the end of the season, each female Japanese beetle can lay about 50 eggs. They live for about 30 to 50 days as adults. Adult beetles will appear the following year if this cycle isn't broken.

When to Control Japanese Beetles

The proper timing for controlling Japanese beetles depends on what stage of the beetle's lifecycle you are trying to attack.

• Hand-picking or spraying with chemical or natural pesticides should be done while the beetles are actively feeding on plants, which lasts roughly a month in late May, June, or July.
• Attacking the larvae stage (the grubs) is usually done in late summer to fall when the grubs are maturing and moving upward to feed on roots.

It's impossible to entirely get rid of Japanese beetles. More will fly in as the current group is killed. And there aren't many natural controls for adult Japanese beetles. Birds aren't partial to them, and although some predatory wasps and flies have been imported, their population isn't large enough yet to control the Japanese beetle problem.

Controlling this pest will require you to use one or several hands-on methods. Remember that adult Japanese beetles are only around for a little over a month, so don't automatically reach for harsh chemicals unless they become a serious problem. 

How to Get Rid of Japanese Beetles

The most effective natural control is to remove beetles from your plants by hand. Brush them off the plants and into a jar of water mixed with dish soap, where they quickly drown. Japanese beetles feed in groups starting at the tops of plants, so filling a jar with them is usually pretty easy. But you will need to do this every few days for the month.

Other methods include physical barrier controls, organic methods, and chemical pesticides.

How to Kill Japanese Beetles With Insecticidal Soap

Insecticide soaps are more effective on soft-bodied insects than beetles, but the soap will kill them if sprayed directly on the Japanese adult beetles.

1. Make Insecticidal Soap

   Insecticidal soap is a mixture of water and the potassium salts of fatty acids. Use a pure liquid Castile soap.

   • Mix 1 gallon of water with up to 4 tablespoons of soap. Start with 1 teaspoon first, gradually adding more soap until it's effective. Too much soap can sometimes harm plants.
   • Another optional but effective addition is cooking oil. Add up to one cup to the solution. Oil coats the insects' breathing apparatus, suffocating them.
     

2. Test Soap Solution on Plant

   Pure castile soap should be safe, but some dish soaps might be too harsh. Before using the spray widely on the plant, test it on a small section first and wait at least 24 hours. Do not use the soap solution if you notice spotting, wrinkling, or browning on leaves.
   

   Warning

   Plants susceptible to damage from soap sprays include tomatoes, cherries, plums, beans, cucumbers, ferns, gardenias, and peas.

3. Spray Insecticidal Soap on Insects

   Concentrate the spray directly on the insect and not the plant. Insecticidal soap has no residual effect, meaning if the beetles are not sprayed directly, they won’t be harmed from walking on or eating sprayed plants after the fact.

How to Use Chemical Pesticides for Japanese Beetles

Any insecticide should be applied carefully, directly on the beetles, since it will also kill other insects.

1. Don Protective Gear

   Wear gloves, long sleeves and pants, eye protection, and a respirator when applying pesticides. Pesticides can be inhaled, ingested, and absorbed by the lungs and eyes, with the skin usually receiving the most exposure.

2. Pesticides for Adult Beetles

   • Try natural or organic methods, such as neem oil or a pesticide containing pyrethrin—a biodegradable substance derived from chrysanthemums. These methods do not have residual effects on the environment versus heavy-duty chemical pesticides.
   • Read the packaging thoroughly to ensure the pesticide you select is effective against Japanese beetles.
     

3. Apply the Solution or Powder

   • When using contact pesticides, thoroughly cover all plant parts, including leaves (undersides, too), flowers, stems, and fruits.
     
   • Ensure that sprays or powders do not drift or run into ponds or water supplies. Pesticides, including organic pyrethrins, are toxic to many aquatic life forms.
     

4. Check for Grubs

   If you have repeated intense infestations of Japanese beetles, check your soil in late summer to see if you have a large grub population.

   • Lift a 1-square-foot section of turf.
   • If there are more than a dozen grubs in this small area, consider treating your lawn with grub control.
     

5. Treat Grub Infestation

   In late summer or early fall, after handling an infestation of adult beetles, consider applying a granular "grubicide." This is a relatively safe chemical pesticide.

   • Follow the label directions and apply carefully.
   • Grub baits are fairly selective pesticides that affect a variety of lawn-damaging beetles and grubs. These baits rarely affect earthworms and other beneficial organisms—except Sevin. Avoid any Sevin product, as this pesticide kills many beneficial organisms, including earthworms.

How to Use Milky Spores and Nematodes for Beetle Control

Milky spores and nematodes are two natural organisms that can be very effective at controlling the larvae of Japanese beetles, although it can take several years to enjoy the benefits fully. They can be used in tandem and applied at the same time.

• Milky spores: These natural live bacteria organisms (Bacillus popilliae) are applied to the lawn. Once grubs become infected by the bacteria, they die within 7 to 21 days. The organisms multiply and spread through the soil as the dead grubs decompose. Once established in the soil, milky spores can protect against Japanese beetles for over 20 years. However, developing the spores thoroughly in colder climates can take as long as five years.
• Nematodes: These tiny microscopic worms naturally live in the soil. Some types are harmful to plants, but the types commonly used for Japanese beetle control (Steinernema spp.) target beetle grubs. Nematodes can be killed by direct sunlight, so apply them on a cloudy day or as night falls. Water them in since this will assist their passage into the soil.

Tips for Controlling Japanese Beetles

The presence of Japanese beetles can also be accompanied by the presence of moles ruining your lawn. The reason is that the moles have arrived to feed on the grubs under the ground. Controlling lawn grubs can, therefore, not only eliminate Japanese beetles but also get rid of your mole problem.

Where Japanese beetles are an ongoing problem, you may want to consider planting your landscape with plants that are less attractive to them. Some plants to consider include:

• Arborvitae
• Boxwood
• Dogwood
• Firs
• Hemlock
• Holly
• Junipers
• Lilac
• Magnolia
• Pines
• Redbud
• Red maple
• Rhododendron